Neutrophil chemotaxis, phagocytosis, and metabolic stimulation were studied in 25 patients with untreated lymphoreticular malignancies, 8 patients with untreated carcinomas, and 8 patients undergoing therapy for lymphoreticular tumors. Phagocytic activity and metabolic stimulation during phagocytosis were comparable to controls in all patient groups. Slight, but significant, differences were found in chemotactic responsiveness of untreated patient groups when compared to controls. In almost all instances, chemotactic responsiveness reverted to normal in most patients studied after therapy for the malignant process. In patients with intact immunologic function these minor differences in chemotactic responsiveness are probably not sufficient to predispose to infection. However, this defect could be additive, and when present in combination with impaired immunity may contribute to compromised host defense.