We studied the evolution of erythrocyte polyamine levels after 17 autologous bone marrow transplants (BMT) in 16 children with malignant diseases. We found that the time to the end of aplasia (0.5 x 10(9) granulocytes per liter) could be divided into 2 distinct periods. The first is characterized by low erythrocyte spermidine (Spd) and spermine (Spm) levels; the second is characterized by normal levels of polyamines. Spd and Spm levels were correlated (r = 0.74) during the second period, but not during the first period or in the control group. Furthermore, the time when Spd concentration was > or = 7 nmol/8 x 10(9) erythrocytes (19 +/- 7) was correlated (r = 0.64) with the advent of end of aplasia (30 +/- 10). We found no correlation between the numbers of CFU-GM and duration of aplasia levels or the duration of period A. The establishment of normal erythrocyte spermidine levels is the earliest index of successful marrow engraftment.