We have prepared a homogeneous, soluble 8.6S species ("8.6S clathrin") from calf-brain coated vesicles. Crosslinking experiments show that this 8.6S clathrin is composed of three heavy chains (molecular weight 180,000) and three light chains (molecular weights 33,000 and 36,000). Each heavy chain is in close contact with a single light chain, and the light chains appear not to be in contact with each other. Intact 8.6S clathrin can reassemble into cages without participation of additional protein species.