Human PMN release lysosomal enzymes (beta-glucuronidase, acid phosphatase) when exposed to immune complexes, but do not release cytoplasmic LDH. The cells remain viable, and failure of LDH to appear in supernatants is not due to selective absorption or inactivation. Release of enzymes is not due to platelet contamination and is only partially enhanced by fresh serum. The selective release of lysosomal enzymes after uptake of complexes resembles that induced by inert particles of zymosan, and can be distinguished from the concurrent release of all enzymes after cell death induced by membrane-lytic crystals of MSU. Uptake of complexes, zymosan, or MSU particles is accompanied by concomitant increases in C-1 oxidation of glucose. Although MSU-induced damage can be retarded by the presence of Tris buffer, immune complexes and zymosan selectively release lysosomal hydrolases in the presence or absence of Tris buffer. Agents which elevate the level, within cells, of cAMP (PGE(1), theophylline, 2-CA) and cAMP itself inhibit the selective extrusion of acid hydrolases from leukocytes without affecting the viability of cells. Leukocytes may respond to immune particles by regurgitating a portion of their lysosomal hydrolases during phagocytosis.