Thirty-four patients undergoing bone marrow transplantation or remission induction for acute non-lymphocytic leukemia were the subjects of a study to determine whether outcome of infection (survival, death) could be related to total complement (TC), complement components, or C-reactive protein (CRP). Serum samples were obtained when the neutropenic patients became febrile, and at intervals thereafter. Significant differences were found between final total serum complement levels, the C3 component of complement, and the C-reactive protein. Multivariate logistic regression demonstrated a significant relationship between the final C3 complement and C-reactive protein levels and the outcome of infection. Changes between initial and final values were also predictive of outcome, suggesting that the magnitude and direction of changes in these measurements may assist the clinician in assessing the success of his prescribed antibiotic therapy. Our data suggest that a test battery comprising serial TC, C3, and CRP measurements may have more predictive potential than each test performed independently.