HeLa cells treated with colchicine show a lengthening of kinetochores lacking an inner layer. Combined EDTA- and ribonuclease treatment (BERNHARD 1969) indicate the presence of ribonucleoprotein in the dense outer layer as well as in the surrounding fine fibrillar mass. Reconstructions from serial sections reveal a band-like enlargement of these layers around the primary constriction during the inhibition of mitosis by colchicine.