Parasitological examination of feces was carried out for 55 patients with diagnosed colorectal cancer before chemotherapy. Except for Cryptosporidium sp., no other intestinal parasites were found in the specimens; moreover, only the patients with watery diarrhea were Cryptosporidium sp.-positive by enzyme immunoassay. Prevalence of infection in the group of patients with diarrhea (23 persons) was 43.5%, whereas it was 18% for the entire group of patients under study. Coproantigens of this parasite were detected primarily in the patients with tumors located on the left side (in the sigmoid and descending colon).