Tetracycline-resistant pneumococci were recovered during a four-month interval from 12 of 252 patients harboring pneumococci. The types of tetracycline-resistant pneumococci which were isolated from these 12 patients varied. Furthermore, three modes of clinical presentation were observed: (1) asymptomatic patients without a history of recent tetracycline therapy, (2) symptomatic patients without a history of recent tetracycline therapy, and (3) symptomatic patients who had recently been treated with tetracycline. We emphasize the existence of an asymptomatic carrier state. There were no distinguishing features of illness caused by tetracycline-resistant pneumococci. Consequently, the diagnosis could only be established by sensitivity studies. These observations warrant a reassessment of tetracycline therapy in patients with pneumococcal infection.