The effects of different phenolic compound concentrations on the fatty acid composition of Lactobacillus plantarum isolated from traditional home-made olive brines were determined. Increasing amounts of caffeic and ferulic acids induced a gradual increase in the amounts of myristic, palmitoleic, stearic and 9,10-methylenehexadecanoic (C17 Delta, where Delta represents the cyclopropane group) acid with a concomitant decrease of lactobacillic acid (C(19)Delta). On the other hand, the addition of tannins induced an increase in the C(19)Delta level at the expense of vaccenic acid content. The presence of acidic phenols and tannins also affected bacterial growth, inducing the most obvious effect with tannin at 1 g l(-1).