Many species of nonhuman primates have been employed to find parasite-definitive host combinations which would allow for investigations on different aspects of schistosomiasis haematobia. Gibbons (Hylobates lar), exposed to moderate numbers of Schistosoma haematobium cercariae, have demonstrated some of the basic features of schistosomiasis haematobia in man. Calcification in schistosomiasis haematobia is variable. Radiologically evident calcification of the bladder was noted in one gibbon. Radio-opaque areas in the bladder corresponded to dense deposits of calcified eggs observed on histological examination. Thus, it seems, bladder calcification, thought to be a later complication of schistosomiasis, can develop fairly rapidly. One of two gibbons killed 11 months after infection had small papillary transitional cell tumours in both ureters. The other had papillary transitional cell tumours covering most of the urinary bladder surface. No invasion of muscle by tumour was present and no metastases were seen.