This paper summarizes a pilot, sequential dose-escalation study of PEG-rHuMGDF in patients with advanced malignancies who had delayed platelet recovery after autologous stem cell transplantation (ASCT). Patients were randomized to receive either placebo (n = 11) or PEG-rHuMGDF at 5 (n = 9), 10 (n = 6), or 25 (n = 7) microg/kg/day by subcutaneous injection for 14 days and were monitored for 5 weeks. Across all treatment groups, eight patients had platelet recovery to > or = 20 x 10(9)/l by day 21. The proportion of patients achieving platelet recovery, the median number of days and units of platelet transfusions were similar for the placebo and the PEG-rHuMGDF groups. PEG-rHuMGDF was well tolerated at all dosages. The incidence rates of adverse events in all groups were similar. No deaths on study, no drug-related serious adverse events, and no development of neutralizing antibodies to MGDF occurred.