Limb buds of 11-day-old mouse embryos were cultured. On day 5,0.1 ml colchicine was added for 3, 6, 12 or 24 h in vitro. 3 or 6 h after application of colchicine, electron-dense granula appear to an increasing extent. These granula can be interpreted as collagen-containing secretion granula and as an indication of a secretion inhibition. The peripheral localization of the granula groups speaks for an effect on the actual discharge of the secretion after having passed the Golgi apparatus. Additional effects of colchicine are fragmentation of the Golgi apparatus and an increased occurrence of bundles of fine filaments. Since only few microtubuli occur in the periphery of the chondroblasts and recent studies indicate an influence of colchicine not only on the microtubule system, a site of action at the functional unity ‘cell membrane-microfîlaments’ is discussed. 12 or 24 h after colchicine application, the contents of the congested secretion granula change. The occurrence of cross-striated structures indicates an activity of procollagen peptidase in the granula in the case of secretion inhibition. In addition, cytolysosomes (autophagic vacuoles) develop. The occurrence of polymorphism of the granula contents under these conditions is attributed to an effect of lysosomal enz