Cytotoxic activity of p-coumaric, caffeic and rosmarinic acids and their Li, Na, K salts in relation to human breast cancer and normal cells were studied by 3-(4,5-domethyffhlazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The acids showed limited toxicity (decrease in survival over 20%). Treatment with Li caffeate resulted in a decrease in the survival of cancer cells (by 20%) but did not show any toxicity in relation to normal cells.