Treatment of severe aplastic anemia (SAA) in Europe between 1970 and 1986 is reviewed. 487 patients received an HLA-identical BMT: results are encouraging and currently suggest a 65% survival. However, many patients cannot be offered this procedure because of the absence of an appropriate donor. Forty-five patients were given a non-HLA identical BMT: results are dependent on the degree of mismatch. Immunosuppression (IS) was given to 509 patients: 50% of these survive. Some mechanisms regulating in vitro hematopoiesis are discussed, together with their relevance in the treatment of SAA.