THE COAUTHOR'S PRELIMINARY INVESTIGATION, REPORTED IN 1978, CONCLUDED THAT THIS TEST WAS MORE USEFUL THAN THE BRENTAMINE TEST, THAT AN AP ACTIVITY LEVEL OVER 20 SIGMA UNITS INDICATED SEMEN PRESENCE, THAT AP ACTIVITY LEVEL DID NOT PREDICT SUCCESS OF TYPING SEMINAL ANTIGENS AND ENZYMES, AND THAT AP ACTIVITY LEVEL COULD OCCASIONALLY BE USED TO DETERMINE THE TIME ELAPSED BETWEEN INTERCOURSE AND TAKING OF THE VAGINAL SWAB. THE PRESENT STUDY CONFIRMED ALL THESE CONCLUSIONS. OF 828 SWABS LACKING DETECTABLE SEMEN, ALL BUT 10 HAD AP LEVELS LOWER THAN 20 SIGMA UNITS. OF 521 SWABS TAKEN WITH SEMEN, ALL TAKEN OVER 2 DAYS AFTER SEXUAL INTERCOURSE HAD NO DETECTABLE SEMEN, WHEREAS ONLY 21 PERCENT OF THOSE TAKEN WITHIN 6 HOURS HAD AP LEVELS UNDER 20 SIGMA UNITS. THE FOLLOWING TWO CHANGES HAVE SIMPLIFIED AND SPEEDED THE TEST WITHOUT LOSS OF INFORMATION: (1) DESCRIBING ALL SWABS WITH VERY HIGH AP LEVELS AS 'GREATER THAN 600 SIGMA UNITS', AND (2) GROUPING TOGETHER ALL SWABS WITH LESS THAN 5 SIGMA UNITS, OF WHICH 84 PERCENT HAVE BEEN SHOWN TO HAVE NO DETECTABLE LEVEL OF SEMEN. TWO FIGURES, ONE TABLE, AND A REFERENCE LIST ARE INCLUDED. (CFW)