Incubation of mixed bovine lens crystallins with 100 mM potassium cyanate causes almost all the protein to form large aggregates. These aggregates are not dispersed by powerful chaotropic agents and are held together by disulphide bonds. Experiments with beta L-crystallin show that carbamylation of this one protein class can bring about the aggregation of other unmodified crystallins. The carbamylated crystallin served as a nucleus for aggregation of other crystallins. These changes are related to the chemical modification of crystallins and the ensuing conformational changes in cataractogenesis.