To the editor: As information on infective endocarditis in intravenous drug users accumulates, its character as an illness with a regional flora becomes increasingly apparent. The recent report of Mills and Drew (Ann Intern Med 84:29-35, 1976) from San Francisco is remarkable for several reasons. First, it adds Serratia to coagulase positive staphylococci (1), Pseudomas aeruginosa (2), and Candida sp. as common or predominant regional pathogens causing endocarditis in intravenous drug users. Second, it depicts similarities between the clinical picture of serratia and pseudomonas infections (2), in that these patients present with infections of both right and left sides of