In connection with synthetic work on insulin a study was made of the behaviour of natural A-chain-Buntesalt isolated from pig insulin after treatment with sodium in liquid ammonia. The A-chain was partially degradated and compounds with different amino acid compositions were built. It was possible to isolate the remaining intact A-chain as tetra-S-sulfonate by chromatography on DEAE-Sephadex with a yield of 55 per cent. This fraction gave, after recombination with isolated B-chain, the same yield of insulin as did A-chain undamaged by sodium.