Neutrophil function and pyogenic infections in bone marrow transplant recipients. In a consecutive entry trial, the incidence and time course of decreased neutrophil function was assessed in 20 patients treated with allogeneic bone marrow transplantation (BMT). The aim of the study was to assess the prognostic value of low neutrophil function for late pyogenic infections. Chemotaxis, superoxide production, and phagocytic-bactericidal activity were studied before and 2, 6, 9, and 12 months after BMT. Skin window migration was quantitatively assessed 2 months after BMT. Infectious complications were recorded prospectively with preset criteria during 1 year. Six of the 20 leukemic patients had defective neutrophil function before BMT. Two months after BMT all 10 patients with greater than stage II graft-versus-host disease (GVHD), and 6 of 10 patients with less than or equal to stage II GVHD had at least one decreased function. At this time, patients with subsequent pyogenic infections had lower chemotaxis (P less than .05), phagocytic-bactericidal activity (P less than .005), and superoxide production (P less than .025) than those without. Defective skin window migration and combined defects were predictive for late pyogenic infections. At 9 months all tests were normal in seven patients surviving without GVHD. In contrast, at 9 months three of three patients, and at 1 year two of three with chronic GVHD had still decreased neutrophil function. In conclusion, neutrophil function is frequently impaired during the first months after BMT. Combined neutrophil defects predispose to pyogenic infections and indicate the patient at risk. 