A case of human cryptosporidiosis, the first one reported in Czechoslovakia, is described. The disease was diagnosed by the presence of Cryptosporidium oocysts in the feces. The methods used independently to identify oocysts were the fecal flotation technique employing a saturated solution of sucrose and the microscopic examination of stained fecal smears. The patient was a 4-year-old boy with watery diarrhea of 5 days' duration who was kept on a diet and treated with a suspension of Endiaron N Spofa. Excretion positivity for Cryptosporidium oocysts in the feces was detectable at 3 and 5 days after appearance of first clinical manifestations. Bacteriological examination was repeatedly negative. This finding leaves little doubt as to existence of human cryptosporidiosis in Czechoslovakia, but what remains obscure is its overall contribution to the etiology of diarrheal diseases encountered in the population.