winter dysentery (wd) is a seasonal infectious disease described worldwide that causes a marked decrease in milk production in dairy cows. in the northern hemisphere, where the disease is classically recognized, bovine coronavirus (bcov) has been assigned as a major etiologic agent of the disease. nonetheless, in the southern hemisphere, an in-deep etiological survey on wd cases had not been carried out. this study aimed to survey for bcov by nested-rt-pcr, rotavirus by polyacrylamide gel electrophoresis (page) and elisa, bacteria by classical bacteriological methods and pcr for virulence factors and parasites by sugar flotation test on fecal samples of 21 cows from a farm during an outbreak of wd in s？o paulo state, southeastern brazil. bcov was detected in all 21 samples, while rotavirus was detected in two symptomatic cows. escherichia coli, yersinia intermedia, providencia rustigianii proteus penneri, klebsiella terrigena and enterobacter aglomerans were detected in samples from both asymptomatic and healthy cows in different associations. the study of e. coli virulence factors revealed that the strains isolated were all apathogenic. cysts of eimeria sp. and eggs of strongyloidea were detected at low numbers in four of the symptomatic cows, with one co-infestation. these results suggest bcov as the main etiologic agent of the cases of wd in brazil, a conclusion that, with the clinical and epidemiological patterns of the disease studied herein, match those already described elsewhere. these findings give basis to the development of preventive measures and contribute to the understanding of the etiology of wd.