During a one-year prospective study, the clinical conditions in which Listeria monocytogenes was isolated from nineteen patients (six females, thirteen males) included meningitis, meningoencephalitis, spontaneous peritonitis, septicaemia, arthritis, pelvic infection and urethritis. All isolates were type 4 serotype. Both apparently well persons and patients with already compromised immune systems were observed. Subtyping of ascitic fluid lymphocytes in one patient with peritonitis showed predominantly T cell subpopulation and no B cells. Most isolates were sensitive to ampicillin, crystalline penicillin and erythromycin. A mortality of 27 per cent was recorded.