Seven young to middle-aged patients with Haemophilus parainfluenzae endocarditis are reported. Three patients had underlying heart disease and three patients had recent events predisposing for endocarditis. The clinical presentation was subacute or acute and new pathologic murmurs were uncommon. Diagnosis was prolonged because of difficulties in isolating the organism. Routine subculturing of blood cultures to chocolate agar with incubation in CO2 is recommended. A prominent complication, occurring in six patients, was major arterial occlusion secondary to emboli. Antibiotic control of infection was difficult and best achieved by the concomitant administration of ampicillin and gentamicin. Killing curves proved useful in assessing antibiotic efficacy. There were two medical failures and one death in the series. It appears H. parainfluenzae endocarditis is characterized by distinctive clinical features, difficult in vitro isolation of the organism, and the necessity for combination antibiotic therapy.