The clinical and microbiologic features of group A streptococcal bacteremia are described in 40 patients, all of whom were seen between January 1982 and June 1983 and all of whom were intravenous drug abusers. Eleven patients had endocarditis (two with left-sided and nine with right-sided), and 29 patients had bacteremia without endocardial involvement. Twenty-seven of the 29 patients without endocarditis had soft tissue infections, primarily groin abscesses. Constitutional symptoms were more severe in patients with endocarditis. The two patients with left-sided endocarditis died despite antimicrobial therapy; all nine patients with right-sided endocarditis and all 29 patients without endocarditis were cured of their infection. A predominant strain of group A streptococcus was identified by serologic typing, suggesting a common source for these cases.