Whipworms from the macaque and baboon were studied by light and scanning electron microscopy. They were identified as Trichuris trichiura, though a slight variation was observed in the length of spicule as compared with the whipworms collected from man. Moreover, a row of small knob-like structures was observed at the base of the pericloacal papillae of T. trichiura from the monkey by scanning electron microscopy. T. trichiura from non-human primates and man has been reported to be morphologically indistinguishable from T. suis. However, this study showed that males of T. trichiura from both the monkey and man can be differentiated from T. suis from the pig on the basis of the presence of a pair of pericloacal papillae and a cluster of small papillae near the caudal end in the former, which is totally absent in the latter.