The purpose of this study was to develop a cost-effective strategy for screening for enteric protozoan infections in homosexual men without gastrointestinal symptoms suggesting infection. One hundred and one homosexual men in Portland, Oregon, each submitted at least one unpurged stool sample; 91% submitted three samples each. Of these, 27% had Entamoeba histolytica, 61% had nonpathogenic protozoa with or without E. histolytica, 36% had a nonpathogen alone, and 3% had Giardia lamblia. Protozoan infection was highly associated with the practice of anilingus (p less than 0.005). Infection with E. histolytica correlated significantly with the presence of nonpathogenic protozoa (p less than 0.005). The following screening strategy was judged to be the most cost-effective: examine one sample first; if E. histolytica is found or if the sample is negative, no further investigation is required; if a nonpathogen is found, one additional sample should be obtained. This strategy had a sensitivity for E. histolytica of 85% and a cost of $136 per case detected.