In order to know the epidemiological, clinical and evolutive characteristics of bacteriemia caused by beta-hemolytic streptococci groups A and B, a retrospective investigation was undertaken of 48 bacteremic episodes observed in adult patients for 10 years (1985-1994). Twenty-two episodes were caused by Group A beta-hemolytic streptococci (GAS) and 26 by Group B beta-hemolytic streptococci (GBS). Patients with GAS bacteremia (GASB) had a lower mean age than patients with GBS bacteremia (GBSB) (p = 0.03). Infection with immunodeficiency virus was more common in patients with GASB than in patients with GBSBA (27 and 4%, respectively; p = 0.04); in contrast, diabetes mellitus was more common in patients with GBSB than in patients with GASB (27 and 5%, respectively) (p = 0.04). Nine (41%) patients with GBSB were i.v. drug abusers; nevertheless, none of the subjects with GBSB were i.v. drug abusers (p < 0.001). The proportion of bacteremia without demonstrable source due to GBS (41%) was significantly higher than that due to GAS (9%) (p = 0.02). Five (23%) patients with GASB and other five (20%) patients with GBSB had fatal outcomes, but only in two (9%) and three (12%) cases, respectively, was death directly attributed to bacteremia. In conclusion, bacteremias caused by GAS and GBS have different epidemiological characteristics but similar prognosis.