In order to assess the effects of schistosomiasis in the prostate gland, seminal vesicles, and the intra-abdominal protion of the vas deferens, we examined these organs at 200 consecutive autopsies of African males. Portions of these organs, as well as of the bladder, were digested in KOH; the proportion of eggs of Schistosoma haematobium found in these organs was: seminal vesicles, 54.5%; spermatic duct, 39.9%; and prostate gland, 20.5%. Eggs of Schistosoma mansoni were rarer in these tissues (bladder, 1%; seminal vesicles, 15.5%; spermatic duct, 8%; and prostate gland, 1%). The mean number of S. haematobium eggs per gram of tissue was substantially greater than for S. mansoni. To compare the histologic technique with that of digestion of tissue, we studied a further 100 consecutive autopsies—77% showed evidence of schistosomiasis by one or the other method. The bladder was affected in 65%; prostate gland, 21%; seminal vesicles, 70%; and the vas deferens in 42%. The detection of schistosomiasis was almost as good by the traditional histologic as by the digestion technique. Neither method revealed all infections. The frequency and severity of the lesions in these tissues was studied by standard histologic technique; tissues from the last 100 consecutive cases showed definite inflammatory lesions, especially in the seminal vesicles, but less than in the prostate gland. In none, however, was the reaction marked. There was good correlation between the mean number of eggs by the histologic and digestion methods, the exception being the prostate gland. No correlation could be shown between the number of eggs and inflammation: only a few eggs may provoke a marked response, or the reverse may occur. However, when inflammatory reaction was present, the average number of eggs per field was higher in every organ. Eggs were found mainly in the muscle layer of the seminal vesicles, but not uncommonly they were present in the mucosa and even in its lumen. The number of eggs did not vary much with the age of the infected person, but after the age of 60 years, the mean number of eggs in the bladder and the seminal vesicles dropped markedly.