ABSTRACT.    Although monkeys and apes are the closest relatives of humans, their intestinal trichomonads have not been thoroughly studied. We have analyzed feces of 53 primate specimen belonging to twelve species and originating from four Czech Zoos. We have established 36 trichomonad strains and have sequenced their SSU rDNA. Phylogenetic analysis of the obtained sequences showed that these strains represent at least seven different species of trichomonads, with most of the isolates belonging to the genus Tetratrichomonas. All strains originating from chimpanzees and gibbons belonged either to the tetratrichomonad lineage 10 (undescribed species known from tortoises and cattle) or to T. buttreyi (lineage 7) which was originally described from pigs. Strains from lemurs belong to the T. gallinarum complex (tetratrichomonad lineage 15), and strains from macaques are closely related with the Tetratrichomonas lineage 11 from wisent. The other strains from greater galagos, macaque, colobus, and lemur represented Pentatrichomonas hominis, Hypotrichomonas sp. and Trichomitus sp. Our results show that primates could be infected with trichomonads from several unrelated host taxa and that the diversity of intestinal trichomonads of non-human primates is far greater than has been previously considered.