Propyl gallate shows little antibacterial activity however it markedly potentiates the activity of meclocycline against Pseudomonas, Proteus, Serratia, Escherichia coli and Klebsiella strains. The potentiating effect of propyl gallate is seen especially with resistant strains whereas sensitive strains of Salmonella do not manifest a potentiating effect on meclocycline by propyl gallate. The mechanism of action of propyl gallate is discussed.