The pharmacokinetics, the safety and the efficacy of purified recombinant human granulocyte colony-stimulating factor (rh G-CSF) expressed in Chinese hamster ovary (CHO) cells were studied in normal healthy adults. Following the single subcutaneous dose, G-CSF levels in sera elevated in a dose-dependent way, with C-max of approximately 140 pg per ml, T-max of 4 hours and T-half of 5 hours at a dose of 10 micrograms per ml. In accord with the elevation, blood neutrophil counts rose promptly and transiently without any changes in the other blood cell counts. Degree and duration of the neutrophilia were apparently proportional to the rh G-CSF dose and, in turn, the G-CSF levels in sera. Single daily injections of rh G-CSF at a dose of 10 micrograms per body per day for 7 consecutive days did not bring on any accumulation of rh G-CSF in sera, and repeatedly induced neutrophilias following every injection. During the course of the injections, the chemiluminescence generating ability of blood neutrophils also rose. Peak value of the transient neutrophilias and level of the abilities tended to go down after 3 or 4 consecutive injections, presumably due to the limited number of mature neutrophils which can be released from the bone marrow in response to rh G-CSF. However, it was found that the M/E ratio becomes higher after the repeated dosing with an increased proportion of myeloid immature cells as well as increase in the levels of both erythroid and myeloid precursor cells in the bone marrow.(ABSTRACT TRUNCATED AT 250 WORDS)