Granulocyte colony stimulating factors (G-CSFs) play a very important role in the current technique of stem cell transplantation. The conventional timing of administration of G-CSF in both mobilization and post transplantation has been right after chemotherapy or right after transplantation. We have studied the effects of timing of administration of G-CSF in 21 patients who had autologous stem cell transplantation for breast cancer, lymphoma or nasopharyngeal cancer. Their stem cells were mobilized by chemotherapy followed by G-CSF, which were given on day +1 or day +5 after chemotherapy. The median peak percentage of CD34 positive cells harvested using both technique were 1.88 and 0.48% respectively. After transplantation, G-CSF were given on day +1 or day +6 after stem cell infusion until neutrophil recovery. The time until bone marrow recovery was significantly longer in the group with delayed administration of G-CSF (10 days versus 8 days). However, there was no difference in duration of neutropenic fever or hospital stay after transplantation. The transplantation outcome was also unaffected. We therefore concluded that G-CSF can be given in the delayed fashion in both mobilizing and post transplantation settings without jeopardizing the outcome and this would result in a significant cost saving.