This method sensitively detected blood-group-substance (BGS) activity in semen. However, it did not detect BGS activity in saliva, urine, breast milk, blood, or vaginal secretions. The concentration of p 84 in semen was independent of the secretion status; therefore, the status can be determined as non-secretor when p 84 but not BGS activity was detected. Dried stains of semen were kept at 4, 26, and 37 degrees Celsius for 8 months, 2 years, and 1 month, respectively to determine the stability of BGS activity on p 84. More than 60 percent of the original BGS activity was recovered from the stain after 8 months at 4 degrees Celsius. About 20 percent of the BGS activity still remained after 1 month at 37 degrees and 2 years at 26 degrees. Finally, BGS activity of p 84 was detectable at ratios of up to one to four in stains with semen mixed with saliva or blood and used for the sources of dried stains. Findings indicated that this sandwich ELISA offers greater sensitivity in determining the ABO blood type of semen samples obtained from sexual assault victims than do existing methods such as the conventional absorption-elution and classical hemagglutination-inhibition tests. Tables, figures, and 7 references (Author abstract modified)