Stool samples from 523 children aged between 3 months and 6 years were examined for Cryptosporidium parvum by means of the direct immunofluorescence technique in March 1996. The specimens were sent to the Federal Public Health Laboratory in Innsbruck from general practitioners and pediatricians and from hospitals in Tyrol and Vorarlberg. The study was performed during the cold season in an area that does not employ surface water for the production of drinking water. Oocysts of cryptosporidia were detected as the sole agent in 4 out of 294 samples (1.4%) taken from children suffering from diarrheal disease, as well as in 1 out of 229 samples (0.4%) of children in the control group. Duration of diarrheal disease varied from 2 days to 4 weeks. In addition, a 75 stool samples from Tyrolean calves were examined for cryptosporidia. Oocysts were detected in 3 out of 75 stool samples (4.0%). Routine examinations for Cryptosporidium parvum in stool specimens of immunocompetent children with diarrhea do not seem to be necessary in Western Austria during the cold season due to the self-limiting course of the infection.