The effect of phenolic compounds, ethyl alcohol, and sodium metabisulphite on the lytic activity of virulent bacteriophage PL-1 on a Lactobacillus casei S strain isolated from a lactic acid beverage fermentation was investigated. Catechin, caffeic, and gallic acids, commercially produced red, white, and champagne tannins, ethyl alcohol, and sodium metabisulphite inhibited plaque formation. Catechin, caffeic, and gallic acids were the most effective inhibitors of plaque formation. Commercially supplied oenocyanin was not effective.