Pluripotent hemopoietic progenitor cells (CFU-GEMM) grow in vitro from marmoset bone marrow using a modified human CFU-GEMM assay. Characteristics of growth are similar to those reported in the human CFU-GEMM assay. The number of CFU-GEMM/10(5) marrow cells from marmoset bone marrow is approximately four times that grown in human marrow in our laboratory. Data concerning EPO and other requirements for growth of CFU-GEMM demonstrate an assay for the pluripotent hemopoietic progenitor in the marmoset. This assay may be useful in designing preclinical primate bone marrow transplant experiments.