Endogenous cytokine release and bone marrow cellularity of cancer patients receiving chemotherapy were investigated to elucidate the effect of high dose medroxyprogesterone acetate (MPA). MPA (1000 mg/day p.o.) was started after the first cycle of chemotherapy in patients with neutropenia. Administration of MPA was stopped a week after the second cycle of chemotherapy. Blood samples and bone marrow aspirations were obtained for granulocyte macrophage - colony stimulating factor (GM-CSF) assay one week after the first and second cycles of chemotherapy. GM-CSF levels and bone marrow cellularities were compared before and after MPA treatment.