The prevalence of cryptosporidia, rotavirus, bovine coronavirus and Escherichia coli F5 (K99) in dairy calves with diarrhea and in healthy calves was established in a limited area served by a veterinary practice. Immuno-chromatographic rapid tests (FASTest Strips) were applied in the field and their results were compared to the ones obtained with standard methods (modified Ziehl-Neelsen stain, antigen-ELISA and cultivation). In 78% of the calves with diarrhea (n=46) and in 29% of the healthy calves (n=14), one or two agents were isolated. Of the diseased calves, 43% excreted cryptosporidia and in 46% rotavirus was isolated. Bovine corona virus and Escherichia coli F5 (K99) seemed to be of minor importance in the investigated population. Compared to the modified Ziehl-Neelsen stain or the antigen-ELISA, the FASTest Strips CRYPTO and ROTA were of very high diagnostic specificity of 100% each and their diagnostic sensitivity was 75% and 57%, respectively. Due to the low number of cases, the results of the FASTest Strips BCV and E.coli-K99 could not be interpreted. Although the diagnostic sensitivity of the FASTest Strips CRYPTO and ROTA--evaluated with standard methods--was not very high, their use in calves with acute diarrhea is recommended.