In the books that Amy Derogatis studies, the abbreviation STD sometimes stands for "sexually transmitted demons," the biblical Song of Songs is read on at least one occasion as a literal instruction manual for sexual stimulation and sex is something to be celebrated, but only in the context of Christian marriage.

Derogatis, 41, is a professor of religious studies at Michigan State University, and she has spent the past few years reading and writing about evangelical Christian sex manuals.

They aren't the prim marriage manuals of the early 20th century, but books that began to appear during the throes of the 1970s Sexual Revolution, churchly cousins to more hedonistic (and, obviously, more secular) works such as Alex Comfort's "The Joy of Sex."

And studying them, said Derogatis, whose first book dealt with how 19th century Protestant missionaries developed a moral basis for American expansionism, "is absolutely not what I expected I would be doing in my research."

It was a student's question that sparked her interest. Five years ago during a class discussion of sexuality and Judaism, a young woman had asked where she could go to learn how Christians - meaning evangelical Christians - are supposed to have sex.

"I sort of made a joke of it," Derogatis said, "and I said, 'I know where you can go to find out how not to have sex, but I'm not really sure.' "

She decided, however, that the question was a good one, "so I ran a Google search and was embarrassed to find there was an avalanche of books on the topic that I was completely unfamiliar with."

She also found that MSU's library had one of the country's better collections.

Peter Berg, assistant director for special collections, said the library has been collecting evangelical Christians books on sex since the early 1990s.

"We felt, listen, this is really interesting stuff that is going on," Berg said. "No one really discusses it, and no one has done any research on it, but it's important, and we should have it, given the history of our collection. And we should have it because somebody is going to discover its importance."

"Voila, Amy Derogatis shows up, and the collection is there for her."

Lots of material

Derogatis spent the summers of 2002 and 2003 just reading, delving into books such as "The Act of Marriage" by Tim and Beverly LaHaye (the same Tim LaHaye who co-authored the popular Left Behind series) and "What Wives Wished Their Husbands Knew About Sex" by Focus on the Family founder James Dobson.

The first surprise in store was "how graphic the material is," she said, "not illustrations, but how directly the manuals talk about sexuality."

The next surprise was how concerned the authors were with "demonstrating God's wish that married heterosexuals enjoy sexual intercourse."

According to these books, she said, the Bible is the best sex manual, and it shows that sex, done properly, is a godly act.

"This celebration of sex within Christian marriage surprised me," Derogatis said. "I expected there to be more warnings against enjoyment of sexuality. That's the baggage I brought to the material."

But she found that, at the same time these books celebrated sex, their authors also were very concerned with drawing lines between those sexual behaviors that are acceptable for a Christian and those that aren't.

Within marriage

And, in this context, acceptable sex is always heterosexual and always between Christian married partners, though there's disagreement on topics such as masturbation, oral sex and sex toys.

"They're very, very directive," Derogatis said. "They really narrow what the imagined possibilities would be for the reader of what a normal man would do or a normal woman would do."

'A wonderful purpose'

"God designed sex," said Dawn Valley, who, together with her husband, Marty, runs the pre-marriage ministry at Riverview Church in Holt. "He has a purpose for it, and, within marriage, that's a wonderful purpose, but our culture has taken it in a different direction."

That's part of the reason couples entering the pre-marriage program get a book called "Intended for Pleasure" by Ed and Gaye Wheat, a guide to sex written by Christian authors.

But Valley said that even some of the young Christian couples with whom she works are surprised by the sex-positive message they're getting.

"We get a lot of questions, especially from engaged couples who are not sexually active together yet, questions like 'Is this OK biblically? Is this OK in Christian marriages?' she said.

"A lot of times they're surprised to find that, what we've found is, anything that doesn't go against biblical standards that's between a man and a woman, if it's OK with the two of you, it's OK."

Opening scholars' eyes

Evangelical sex manuals were not particularly well studied in academia, and Derogatis' first article on the subject (called, perhaps predictably, "What Would Jesus Do?") got her a fair bit of attention.

She's developing a second article - on sexualized understandings of demon possession - and is working gradually on a book tentatively called "Saving Sex."

Her research "opens scholars' eyes," said Philip Goff, director of the Center for the Study of Religion and American Culture at Indiana University-Purdue University Indianapolis.

"We tend to think of evangelicals and fundamentalists as puritanical," he said. "They're always talking about abstinence, no sex outside of marriage, no gay sex.

"In these books, and she's really the first one to go through them all thoroughly, you find out just how important sex is in their lives."