Endemic infection in male surgical wards has been studied during three periods. There was some infection due to gram-negative bacilli, though Staphylococcus aureus remained as the single most important pathogen even in the absence of epidemic spread. Beta haemolytic streptococci were isolated in large numbers from the lesions of four patients with deep wound infection. Changes introduced in the pattern of post-operative care reduced sepsis due to Staph. aureus, reduced the severity of wound infection and apparently decreased the need for antibiotic therapy. Patients who became infected were retained in hospital longer than those who escaped clinically apparent infection.