The prevalence of Cryptosporidium infection in patients who are on chronic hemodialysis due to end-stage renal failure is investigated and compared with the incidence in the healthy population. Stool specimens of 74 adult hemodialysis patients treated on an outpatient basis and 50 healthy individuals are examined for Cryptosporidium oocysts by using the modified acid-fast method. While 20.27% (15/74) of patients in the dialysis group had Cryptosporidium oocysts in their stools, none (0/50) of the controls had such an infection (p < 0.001). Ten of 15 patients who had Cryptosporidium oocysts in their stool specimens were asymptomatic and the remaining 5 had diarrhea. Four of these 5 diarrheic patients had Cryptosporidium oocysts in their stools and 1 had both Cryptosporidium oocysts and Giardia trophozoites. Since hemodialysis patients with chronic renal failure are candidates for renal transplantation, general preventive measures against infection must be taken and these patients must be screened for their carrier state before transplantation.