ABBREVIATIONS

Circulating granulocyte/macrophage progenitor cells (CFU-GM) were assayed serially during remission in 17 patients with acute leukaemia (9 ALL, 8 AML). In patients with ALL receiving cyclophosphamide, 6-mercaptopurine and methotrexate, CFU-GM numbers were significantly lower than in normal individuals; cycles of 'reinduction' chemotherapy (vincristine, prednisolone) caused a 10-fold increase in CFU-GM per ml of blood. In 2 ALL patients a substantial increase in CFU-GM numbers preceded the morphologically detectable relapse. In patients with AML receiving repeated courses of cytosine-arabinoside and 6-mercaptopurine, circulating CFU-GM were likewise reduced. In 6 patients who relapsed, a further reduction of CFU-GM was seen. A complete absence of circulating CFU-GM was observed in 10 of the 23 investigations performed within 6 weeks prior to the morphologically detectable relapse, while such a 'zero'-growth occurred in only 1 of 54 experiments performed during stable remission. In summary, in patients with ALL in remission, circulating CFU-GM are increased following treatment with vincristine and prednisolone. In patients with AML, declining numbers of circulating CFU-GM may predict an imminent relapse.