The authors report the results of the reaction of Sabin-Feldman carried out on the serum of 101 dogs in a süburb of Rio de Janeiro. They found a negative result in 21 dogs (20,8) and a positive result in 80 (79,2%). The titres of the reaction were considered positive from the dilution 1:16 and no positive result was found in an equal dilution or higher than 1:4096. The differences in the proportions of the negative and positive titres in relation to the sex of the animais were not significant. As to age, a significant increase in the proportion of positive results ivas observed among dogs of equal age or more than 5 years, this increase having been more evident in dogs of equal age or more than 7 years. Among the positive titres, the proportion of dilution 1:64 was significantly higher in the dogs of equal age or more than 7 years, when compared to that of the younger dogs. This result demonstrates that it was mainly because of this titre 1:64 that increased the proportion of positive dogs in the group of animais of 7 years or older. The predomiinance of a positive titre which is not high in this group of animais brings us to the supposition that dogs in general become infected chiefly when younger