Two algorithms for screening sera for antibody to human immunodeficiency virus type 1 were compared for their efficiency in identifying a true-positive sample in a population with heterogeneous risk factors, using the criteria of specificity and positive predictive value (PPV). In the first algorithm, all sera were screened by using a single enzyme immunoassay (EIA) kit, and a specificity of 98.6% and a PPV of 69.3% was calculated for true-positive sera. The second algorithm employed two different EIA kits in parallel to screen each sample. In the first instance, a specificity and a PPV of 100% was calculated if a positive sample was defined as reactive by both EIA kits; in the second, a specificity of 99.97% and a PPV of 99.4% was obtained if this criterion was extended to include a combination of one reactive and one equivocal result obtained with the two EIA kits.