We evaluated the timing and pattern of changes in the complete blood cell count that preceded marrow recovery during 107 consecutive episodes of fever and neutropenia in 64 children with cancer. Four measures derived from serial daily measurement of the complete blood cell count were evaluated: total leukocyte count, absolute neutrophil count, absolute phagocyte count, and platelet count. During 70 (65%) of these 107 episodes, patients were discharged with an absolute neutrophil count of fewer than 500 cells/mm3; 24 patients were discharged from the hospital despite an absolute neutrophil count of fewer than 100 cells/mm3. During all but one of these 70 episodes, however, signs of early marrow recovery were present before discharge; sustained increases were observed in these patients' leukocyte, absolute neutrophil, absolute phagocyte, and platelet counts 2 or more days before their discharge in 41%, 49%, 50%, and 39% of cases, respectively. Although they were neutropenic at discharge, most patients had signs of multilineage marrow recovery at that time; 59 of 70 had increases in three of four of the measurements that we studied. None of the 69 patients who had evidence of marrow recovery at discharge had recurrence of fever. We conclude that children with cancer who were hospitalized for fever during periods of neutropenia have increases in the peripheral blood cell count that herald imminent bone marrow recovery, often several days before the absolute neutrophil count recovers to 500 cells/mm3. Our success in discharging such patients before resolution of neutropenia suggests that further controlled trials are needed to evaluate the safety and feasibility of cessation of antibiotic therapy and early discharge from the hospital.