Chromatographic systems are described which are suitable for the examination of procaine penicillin G preparations which may contain, in addition to procaine and penicillin G, the degradation products p-aminobenzoic acid, ethyl p-aminobenzoate, benzylpenicilloic acid, and benzylpenillic acid. Further decomposition of penicillin G occurs when alcoholic solutions are used for spotting the chromtograms, the corresponding alkyl α-D-penicilloate being formed, whereas only penicillin G was detected when freshly prepared aqueous solutions were used. However, in aged aqueous solutions the rate of decomposition of penicllin G increased markedly and two new spots, due to benzylpenicilloic acid and benzylpenillic acid, were detected on the chromatogram.