Twenty-nine patients were treated with single or combined high-dose melphalan therapy followed by autologous bone marrow transplantation. Hematopoietic recovery from these treatments was studied. No correlation was found between the number of GM-CFC infused and the time required for hematopoietic recovery. It is suggested that this correlation is only demonstrable for low 'doses' of infused bone marrow cell and/or GM-CFCs. The role of bone marrow cell preservation techniques was examined and results were similar for fresh and cryopreserved bone marrow. The erythrocyte, lymphocyte and granulocyte levels of the patients reported here reached a normal or subnormal hematological steady state 3 months after autograft. Our results confirm the value of cryopreservation techniques. Hematopoietic recovery was short and of the same duration whether the patients were given single or combined high-dose melphalan before autologous bone marrow transplantation. These results also demonstrate the value of such transplantation in shortening the myelosuppression caused by high-dose chemotherapy.