Low course doses of cyclophosphamide (1.9 +/- 0.2 g) were given to postsplenectomy patients with grave aplastic anemia (GAA). A total of 27 patients aged 14-42 years were treated, 27 control GAA patients did not receive cyclophosphamide. The cyclophosphamide therapy was controlled by T-lymphocyte functional activity assessed in active rosette formation test with levamisole in vitro. 19 (70.3%) patients were treated twice. The remission was achieved in 22 patients (81.5%), partial response was in 1 patient (3.7%), 4 patients died (14.8%). In control subjects the remission was recorded only in 4 subjects, 23 patients died 3 to 12 months after splenectomy. It is evident that low-dose courses of cyclophosphamide are highly effective in case of control over immunological activity of the pathological process.