PITTSBURGH (AP) _ There was shrieking, giggling and blushing from high school students when a teacher asked them to ``pick a partner who you'd like to exchange body fluids with.''

The request was nothing lurid. It was merely part of an experiment to show the students how fast the AIDS virus can spread.

Thirty students each swapped cups of chemically treated water with three others. Color changes showed that about three of every four students became ``infected'' with mock HIV.

The results stopped the giggling _ and taught a lesson Wednesday. Donte Taylor, 15, called it an ``eye opener'' for teens.

``It scares me,'' he said. ``It's better to just not do anything: abstinence.''

Revelations this week that a New York man may have knowingly infected at least nine women and girls as young as 13 make the lesson especially timely, organizers said.

The exercise was part of a curriculum on AIDS offered to 3,000 teachers who are meeting in Pittsburgh for the three-day convention of the National Science Teachers Association, which officially begins today. Since publication last spring of the curriculum's book and video, both titled ``The Science of HIV,'' thousands of teachers have requested them, the association said.

And despite references to rectal tears and vaginal fluid, nobody involved with the project can recall a single complaint about unsuitable contents.

``I think there are a fair number of parents who are relieved that it's being taught,'' said Sharon Nelson, a teacher at Waunakee High School in Waunakee, Wis., who has used parts of the curriculum in her classes.

The key is focusing on scientific principles behind HIV infection, ``not a moral judgment on what you should or should not be doing,'' said Michael DiSpezio, who wrote the curriculum with funding from Abbott Laboratories, a medical and pharmaceutical manufacturer in Chicago. In his hourlong lesson with 70 students at Taylor Allderdice High School, DiSpezio used Lego blocks and color drawings to describe how proteins are built in a cell, how a virus attacks and why HIV is impervious to disease-fighting cells.

``If somebody is telling them to do something and not explaining why, that doesn't have as much clout,'' said DiSpezio, who previously worked as an eighth-grade teacher and a scientist who studied parasites.

In the water-swapping experiment, DiSpezio asked 30 students to each take one cup of water, dump the liquid into a friend's cup and take half back again, then swap with two more partners.

Water in only four of the 30 cups was treated beforehand with a chemical representing HIV. When DiSpezio squirted a drop of another chemical into it, the water in the ``infected'' cups turned red.

He tested each student's cup, and 23 turned red. Students yelled and gasped as the number of infections mounted.

``People my age, they don't think it can happen to them. They think you have to be older to get AIDS,'' said Latasha Drummond, 16, who became ``infected'' in the experiment.