In autologous stem cell transplantation the duration of aplasia may be particularly long. We studied 27 children with a median age of 5 years (1-16), who received 31 autologous grafts, seven of them receiving both bone marrow and peripheral stem cells. Five were transplanted with blood derived stem cells only. The median number of nucleated cells (NC) grafted was 1.04 x 10(8)/kg body weight (range 0.09-6.72). The median number of granulocyte-macrophage progenitors (CFU-GM) transfused was 0.66 x 10(4)/kg body weight (range 0-11.8). The numbers of NC correlated with the CFU-GM numbers (p less than 0.001), and were inversely correlated with time to recover 1 x 10(9)/l leukocytes and 0.5 x 10(9)/l granulocytes (p less than 0.01), as well as with the appearance of reticulocytes (p less than 0.05). Moreover, the logarithm of the CFU-GM numbers transfused was linearly correlated with the time to recover 1 x 10(9)/l leukocytes and 0.5 x 10(9)/l granulocytes (p less than 0.001), respectively. There also existed an inverse correlation with the first appearance of reticulocytes in the peripheral blood (p less than 0.01). No correlation could be detected with the duration of platelet transfusion dependence. Based on our findings a prediction of time to recover leukocytes, granulocytes and reticulocytes is feasible before grafting with autologous bone marrow and peripheral stem cells.