Antibody-dependent cellular cytotoxicity (ADCC) against Raji cells was used as a model system to investigate the polymorphonuclear leukocyte (PMN) mechanisms involved in tumor cell lysis. PMN killed target cells by nonoxidative means, as indicated by the following observations: PMN from patients with chronic granulomatous disease (CGD), defective in their metabolic burst, lysed Raji cells normally; impairment of the oxidative metabolism of normal PMN by phenylbutazone did not affect ADCC. Rosenthal's inhibitor of phospholipase A2 completely prevented the lysis, suggesting the involvement of this enzyme in the target cell damage. The inhibition of the Raji cell glutathione redox cycle by carmustine [1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)] increased cell susceptibility to PMN-mediated ADCC. This increment of lysis was related to oxidative killing systems. In fact, CGD PMN had an ADCC against BCNU-treated Raji cells lower than that mediated by normal PMN, but comparable to that observed with untreated targets, and phenylbutazone reduced the lysis of BCNU-treated Raji cells by normal PMN to the level observed with the use of untreated targets. The remaining ADCC against BCNU-treated Raji cells mediated by CGD PMN and by normal PMN in the presence of phenylbutazone was suppressed by Rosenthal's inhibitor. Thus PMN killed sensitized BCNU-treated Raji cells by use of both oxidative and nonoxidative means. The results indicate that the interaction of sensitized Raji cells with PMN triggers simultaneously oxidative and non-oxidative potentially lytic systems and the mediator(s) of Raji cell lysis actually operating may depend on the metabolic state of the target cells themselves. Therefore, the lysis of sensitized tumor cells might not reflect the simple effect of PMN tumoricidal systems; rather it should be regarded as a result of an inability of the target cells to escape the various PMN cytolytic mechanisms.