In this study effects of incubation of sheep blood agar medium in aerobic conditions and incubation of sulfamethoxazole-trimethoprim containing sheep blood agar medium in 5 to 10% CO2, of the isolation of group A beta hemolytic streptococci from throat cultures were compared. 608 throat swab specimens were studied. Each agar medium was evaluated after 24 and 48 hours of incubation period. The aerobic incubation of sheep blood agar plates for 24 hours yielded 108 (17.7%) strains of beta hemolytic streptococci, of these 96 (15.8%) strains being group A. 113 (18.5%) strains of beta hemolytic streptococci were isolated after 48 hours of incubation and 100 (16.4%) of these were group A. The number of beta hemolytic streptococci isolated in 5 to 10% CO2 atmosphere for 24 hours was 62 (10.2%), and 57 (9.3%) of these were group A. When the incubation period was prolonged to 48 hours, the total number of beta hemolytic streptococci isolated increased to 82 (13.5%) and 76 (12.5%) of these were determined as group A. The difference between these two combinations was significant for 24 hours of incubation, but not significant for 48 hours of incubation. The highest isolation rate for group A streptococci was achieved in aerobic incubation of sheep blood agar plates for 48 hours.