n-AMYLPENICILLIN was first prepared in an impure state by Catch, Cook and Heilbron1 by the catalytic hydrogenation of Î"2-pentenylpenicillin, the product being characterized by conversion to the penillic acid and by the identification of n-caproic acid among the products of hydrolysis of the latter substance. The presence of n-amylpenicillin in the mixture of penicillins formed by the submerged fermentation of P. chrysogenum Q 176 has also been reported ; but the isolation of the pure penicillin has not yet been recorded. This penicillin has now been isolated in the pure state and characterized.