One hundred and one donors who had received filgrastim (rhG-CSF) for the purpose of donating either granulocytes or peripheral blood stem cells (PBSC) for their relatives more than 3 years ago were contacted. All donors had received daily rhG-CSF at a median dose of 16 microg/kg/day (range 3-16) for a median of 6 days (range 3-15 days). All collection procedures were completed and short-term side-effects of rhG-CSF were mild in the majority of the donors. At a median time interval of 43.13 months (range 35-73), the donors were contacted to assess whether adverse effects related to rhG-CSF administration had occurred. Prior to rhG-CSF two donors had cancer, one had a myocardial infarction, one was hepatitis C virus positive, one had a history of sinusitis, one had Graves' disease and two had arterial hypertension. None worsened with the rhG-CSF administration but the donor with a history of infarction had an episode of angina following apheresis, and the donor with Graves' disease had a stroke 15 months after rhG-CSF. Two pregnancies occurred after the rhG-CSF administration and one donor was 2-3 weeks pregnant during rhG-CSF treatment. Three pregnancies resulted in two normal births and one in a spontaneous abortion of a pregnancy which occurred more than 2 years following rhG-CSF. In the time following rhG-CSF administration two donors developed cancer (breast and prostate cancer) at a follow-up of 70 and 11 months, respectively. One donor developed lymphadenopathy 38 months after the rhG-CSF, which spontaneously resolved. Blood counts were obtained in 70 donors at a median follow up of 40.4 months (range 16.8-70.8). Hematocrit was 43% (median, range 36.8-48), white blood cells were 5.7 x 109/l (median, range 3-14), granulocytes 3.71 x 109/l (median, range 1. 47-10.36), lymphocytes 1.67 x 109/l (median, range 0.90-3.96), monocytes 0.46 x 109/l (median, range 0.07-0.87) and platelet counts were 193.0 x 109/l (median, range 175.0-240.0). This study indicates that short-term administration of rhG-CSF to normal donors for the purpose of mobilizing the PBSC or granulocytes appears safe and without any obvious adverse effects more than 3 years after the donation. Bone Marrow Transplantation (2000) 25, 85-89.