1. Attempts were made to demonstrate the presence of pyridoxal phosphate in the rat liver system catalysing the αβ-elimination of l-serine O-sulphate. 2. Methods designed to resolve protein-bound cofactor, spectroscopic examination of a purified enzyme system and attempted reactivation of apo-(alanine aminotransferase) failed to demonstrate the presence of pyridoxal phosphate. 3. The activity of the αβ-eliminating system remained constant in vitamin B6-deficient animals even though the activities of other pyridoxal phosphate-dependent systems fell markedly. 4. The metabolism of l-serine O[35S]-sulphate in vivo appears to be normal in vitamin B6-deficient animals. 5. No incorporation of tritium into the αβ-eliminating system occurred after administration of tritiated pyridoxine to experimental animals.