The authors describe an evaluation programm of Sabin oral vaccine against Poliomyelitis in a semi-rural community, ábout 50 Km away from Rio de Janeiro. 114 children (age between 3 months to 3 years) have been vaccinated (Table 1) with trivalent vaccines (500.000, 200.000 and 300.000 TCD50 per dose for type 1, 2 and 3 respectively) in a total of three doses, with 8 weeks intervals. Blood samples have been collected by venous puncture or filter paper discs, by the first and the third dose and 9 weeks after this third dose. The conversion rate obtained (serum dilution 1/8) reaehed 82,7% for type 1, 98,5% for type 2 and 75,4% for type 3 (Table 2), after 3 doses of vaccine. The age distribution of the children without antibodies, after 3 doses of vaccine (Table 3) shows that the age group between 1 and 2 years presents the worse conversion rate. It is pointed out that the life conditions of the studied population are similar to the ones in the rural parts of the country; a comparative evaluation in a urban area woud be very desirable. The authors suggest that the increase of the amount of Poliovírus type 1, present in the vaccine, most probably would improve the conversion rates in populations like in this paper. Quantitative studies about Enterovirus antibodies in the studied population will be presented later.