Serum samples from 134 dogs from 22 cattle dairy farms in the northern region of Parana State, Brazil, were tested for antibodies to Neospora caninum in an indirect fluorescent antibody test. Antibodies (> or = 1:50) to N. caninum were found in 29 (21.6%) of the 134 dogs, and seropositive dogs were found on 14 (63.6%) of the 22 dairy cattle farrms. The antibody titers of dogs were 1:50 (3 dogs), 1:100 (7 dogs), 1:200 (7 dogs), 1:400 (6 dogs), and > or = 1:800 (6 dogs). The low prevalence (9%) in < 1-yr-old dogs compared with the 2- to 3-fold higher prevalence in older dogs (17-29%) suggests postnatal exposure to N. caninum infection.