Seventy-four patients with acute pure monoblastic leukaemia treated between 1970 and 1978 were studied retrospectively. The disease was usually hyperleucocytic and tumoral in character. It occurred with equal frequency in subjects of both sexes and at all ages, with peaks at the two extremes of life. Rubidazone gave a high percentage (75%) of complete remissions, but the prognosis remained sombre, with a mean survival time of 200 days. The incidence of meningeal relapses was reduced by prophylactic measures at central nervous system level, but gingival and cutaneous relapses were frequent. The possibility of bettering the present modest therapeutic results by more intensive chemotherapy is discussed.