Serum samples (n = 204) from 124 white-tailed deer (Odocoileus virginianus) in northeastern Minnesota (USA) were collected from 1984 through 1989 and tested for antibodies to six serovars of Leptospira interrogans (bratislava, canicola, grippotyphosa, hardjo, icterohemorrhagiae, and pomona) using a microtiter agglutination test. Eighty-eight (43%) sera were positive at greater than or equal to 1:100 for antibodies against serovars pomona and/or bratislava; none was positive for any of the other four serovars. None of the 31 sera collected in 1984-85 was positive, whereas all 54 sera collected from 1986 through 1988 had titers of greater than or equal to 1:100. During 1989, only 34 (29%) of 119 sera had titers of greater than or equal to 1:100. Based on these results, we believe there to be wide variability in exposure of Minnesota deer to Leptospira interrogans.