Six patients with acquired aplastic anaemia were treated with cyclosporine (5 mg/kg/day) either alone or in combination with corticosteroids. A favourable response was observed in 4, including 2 patients presenting with an absolute granulocyte count of less than 0.2 x 10(9)/l. The 6th patient showed no effect after 6 wk of therapy and was thereafter successfully treated with anti-thymocyte globulin (ATG). Side effects of cyclosporine therapy were minimal (maximum follow-up 20 months). Temporary discontinuation of the drug in 1 patient resulted in a relapse which responded to reinstitution of therapy. Our results indicate that cyclosporine may be an effective, well-tolerated agent in acquired aplastic anaemia even in previously untreated patients with severe neutropenia.