2697 persons professionally exposed to leptospira working in contaminated waters and grounds or due to contact with infected animals or their products were seroepidemiologically examined. It was established that the presence of leptospirosis in certain categories of examined persons is three to more than ten times higher in relation with it's presence in the control groups. The most frequent serotype was Leptospira pomona. None of the seropositive persons gave data about having leptospirous infection which might be the consequence of asymptomatic infection or unidentified and not registering of the clinically manifested diseases.