We have studied the effect of colchicine and related compounds on secretion of enzymes by thioglycollated-elicited mouse peritoneal macrophages in culture. Colchicine stimulated secretion of inducible neutral proteinase activities of elastase (EC 3.4.21.11), collagenase (EC 3.4.24.3), gelatinase (pepsin B; EC 3.4.23.2), and azocaseinase 2- to 6-fold for a period of several days, but inhibited the production and release of lysozyme (mucopeptide N-acetylmuramoylhydrolase; EC 3.2.1.17), a noninducible macrophage secretory product. Parallel changes were observed in cell morphology and secretion after treatment with colchicine, Colcemid, and vinblastine, but not with lumicolchicine, and these effects could be gradually reversed by withdrawal of colchicine. Cytochalasin B also stimulated secretion of elastase 2- to 3-fold but did not influence release of lysozyme. These results demonstrate that tubulin-binding drugs may have opposite effects in macrophages than those usually reported for other experimental systems and also provide evidence for the nonparallel discharge of different macrophage secretion products.