The conformation of clathrin light-chains along the proximal arm of the clathrin triskelion was studied by using rabbit anti-(light-chain peptides) to inhibit the binding of a mouse monoclonal antibody against an epitope in the amino-terminal region. Prior incubation of triskelions with rabbit antisera raised against the extreme carboxyl-terminal of the light-chains partially inhibited binding. The inhibition was largely removed when tested on light-chains that had been freed from triskelions. This suggests that when the light-chains bind the heavy-chain, they adopt a conformation in which the amino and carboxyl-terminal domains are not fully extended, but fold such that these two domains face each other.