Case I: A middle-age homosexual male developed AIDS with Pneumocystis carinii pneumonia (PCP) and esophageal candidiasis in 1986 during his stay in an European country about five months prior to transfer to Tokyo Metropolitan Komagome Hospital, Tokyo, in 1987. He was also diagnosed as having cryptosporidiosis presenting with mild diarrhea a month following the diagnosis of PCP. Diarrhea was successfully treated with spiramycin. On transfer to Tokyo Metropolitan Komagome Hospital, he was febrile but had no diarrhea. Serum HIV and TPHA were positive and his blood lymphocyte subset T4a was markedly decreased. On the 13th day after transfer to the hospital, watery diarrhea appeared. Cryptosporidium oocysts were detected from the feces taken on the 17th hospital day. The patient died of Escherichia coli septicemia on the 38th hospital day. Autopsy finding yielded Cryptosporidium infection widely spread over the stomach, ileum, bile and pancreatic ducts. Case II: A 31-year-old previously healthy female presented with abrupt onset of mucous stool five times daily. Mucous passage continued on the subsequent days despite administration of loperamide, and the passage increased to 20 times daily with mucous to watery diarrhea associated with mild abdominal cramps and nausea on the 4th day after onset of illness. On the 6th day of illness, she visited Tokyo Metropolitan Komagome Hospital. She denied close contact with pet animals or contact with any person presenting diarrhea. She had no recent history of travelling anywhere outside Tokyo. On examination she was an apparently healthy woman except for a slightly distended abdomen with localized tenderness in the right upper quadrant.(ABSTRACT TRUNCATED AT 250 WORDS)