Four hundred and five serum samples were drawn from cows with reproductive problems which were not vaccinated against leptospirosis from 21 dairy farms. Three distinct geographic regions were determined and the farms were also classified considering the production system, based on technological, zootechnical and sanitary resources. A total of 277 positive reactions were observed, corresponding to 68.39% of the samples. The predominant serovar was hardjo, reactive on 85 samples (20.98%), predominant on nine farms and observed on 17 farms (80.95%). It was observed the predominance of hardjo in all studied regions and on properties classified as type "A" (22 samples) and type "B" (49 samples). The role of this serovar on bovine leptospirosis in Brazil compared with other countries is discussed.