Four platinum compounds, cis-dichlorodiammineplatinum, dichloro- 1,2-benzenediamine-N,N'-platinum, cis-dichlorobis-(cyclohexylamine)platinum and cis-dichlorobis(cyclopentylamine)platinum, were studied for their toxicity toward myelocytic progenitor cells (CFC assay) and pre-antigen reactive cells (P-PFC assay) in murine bone marrow and toward antigen reactive cells in the mouse spleen (MD-PFC assay). It was demonstrated that each of the platinum compounds markedly suppressed the ability of splenic antigen reactive cells to generate antibody producing cells (MD-PFC) 3 days after i.v. injection. At the same time, certain doses of each of the platinum compounds induced selective recovery of the preantigen reactive cells (P-PFC) and myelocytic progenitor cells (CFC) in the bone marrow with a pattern that was unique for each compound. It was also demonstrated with cis-dichlorodiammineplatinum that the recovery for both bone marrow precursor cell populations was multiphasic with time. In general, the results indicated that the platinum compounds induced unique patterns of immunosuppression with relatively minor hemopoietic toxicity.