In 1992 blood samples were taken from 630 forestry workers in the state of Brandenburg, Germany, and an inquiry about tick bites and possible symptoms of Lyme borreliosis carried out in order to determine the seroprevalence of the disease. To estimate the rate of seroconversion within six months, 406 of the individuals were investigated a second time. IgG and IgM antibodies against Borrelia burgdorferi were detected in serum using an indirect immunofluorescence assay (IFA) and an immunoblot assay (IBA). Fifty-three percent of the forestry workers reported suffering a tick bite, 8% of whom recalled an erythema after the bite. Positive results were found more frequently in the forestry workers than in a control group of 200 healthy blood donors in both the IgG-IFA (8% vs. 4%, p < 0.05) and the IgG-IBA (18% vs. 5%, p < 0.05). The detection of IgG antibodies correlated with a tick bite and erythema history. There was a tendency of lower seropositivity by the IgG-IBA in individuals who treated the ticks before removal with chemicals or other agents compared to those without such treatment (16.8% vs. 23.9%, 0.05 > p < 0.1). Likewise, there was a tendency of lower seropositivity by the IgG-IFA in individuals being treated with antibiotics for other reasons compared to untreated individuals (3.15% vs. 8.9%, p < 0.05), although the two groups did not differ in the IgG-IBA (13.8% vs. 18.5%, p > 0.1). The rate of seroconversion within six months ranged from 5 to 7%. It is concluded that forestry workers in Brandenburg, Germany, are at risk for infection with Borrelia burgdorferi, but clinical signs of infection are rare.