A sample of 415 members of the Kaiser Foundation Health Plan (KFHP) were tested for intestinal protozoa. This parasite survey group was found to be comparable in age distribution, sex and ethnic background with the membership at large. Gastrointestinal complaints were no more numerous in this group than in a large series of KFHP members taking multiphasic examinations. Because KFPH membership included, at the time of the survey, approximately 27 percent of all residents of the San Francisco Bay Area, the membership may be considered approximately representative of the entire area. Fourteen percent of persons were found to be infected with one or more intestinal protozoan parasites, while 5.5 percent harbored potentially pathogenic sorts. Entamoeba histolytica was found in 0.7 percent of those surveyed, Giardia lamblia in 1.7 percent and Dientamoeba fragilis in 3.1 percent.