The complex effects of hematopoietic growth factors (granulocyte and granulocyte-macrophage colony-stimulating factors and interleukin 3 and interleukin 1 beta) following myeloablation in juvenile male cynomolgus monkeys was studied. Since the effects of a given cytokine in vivo do not necessarily reflect the in vitro situation, and since cytokines are frequently species specific, extrapolation from rodent models to man may be fraught with inaccuracies. A primate model, therefore, was developed which has provided useful preclinical information on hematopoietic responses, dose response relationships and toxicities associated with administration of recombinant hematopoietic growth factors. This information has direct application to human trials.