Serum samples of dairy cows from the region of the municipality of Pitangueiras, State of São Paulo, were investigated for the possible presence of precipitating antibodies against the gp51 antigen of Enzootic Bovine Leukosis. Blood samples were obtained from animals belonging to seven rural properties which were followed up on a yearly basis, from 1992 to 1995. A total of 140 serum samples were analyzed in 1992. Of these, 24 (17.1%) reacted positively, 21 (15.0%) were suspect and 95<br />(67.9%) were negative. In 1993, of the 122 samples tested 25 (20.5%) were positive, 8 (6.6%) were suspect and 89 (72.9%) were negative. In 1994, of the 135 samples tested, 45 (33.3%) were positive, 19 (14.1%) were suspect and 71 (52.6%) were negative. Finally, 119 samples of serum were investigated in 1995, 60 of which (50.4%) were positive, 11 (9.2%) were suspect and 48 (40.4%) were negative.These results demonstrate that a sharp increase in the prevalence of Enzootic Bovine Leukosis occurred during the experiment. From the viewpoint of Animal Sanitary Defense, the growing dissemination of the disease in the studied population serves as a warning about the epidemiologic behavior and about the evolution of the diffusion of the disease in Brazil.<br /><br /> | Anticorpos précipitantes contra o antígeno gp51 do vírus da Leucose Enzoótica Bovina foram pesquisados em amostras de soros de vacas leiteiras da região do município de Pitangueiras, no Estado de São Paulo. As amostras sanguíneas eram de animais provenientes de sete propriedades rurais que foram acompanhadas anualmente de 1992 até 1995. Durante o ano de 1992 foram analisados 140 soros, dos quais 24 (17,1%) eram reagentes positivos, 21 (15,0%) suspeitos e 95 (67,9%)<br />negativos. Em 1993, dos 122 soros testados, 25 (20,5%) foram positivos, 8 (6,6%) suspeitos e 89 (72,9%) negativos. No ano de 1994 foram testadas 135 amostras, das quais 45 (33,3%) eram positivas, 19 (14,1%) suspeitas e 71 (52,6%) negativas. Finalmente, em 1995, foram analisadas as amostras de 119 animais sendo que 60 (50,4%) eram positivas, 11 (9,2%) suspeitas e 48 (40,4%) negativas. Os resultados obtidos evidenciam que no decorrer do experimento houve um nítido<br />aumento na prevalência da Leucose Enzoótica Bovina com o passar do tempo. Sob o prisma da Defesa Sanitária Animal, a crescente disseminação da doença na população estudada serve como alerta sobre o comportamento epidemiológico e sobre a evolução na difusão da enfermidade em nosso meio.