The protective effect of anthocyanidins against the toxicity induced by linoleic acid hydroperoxide (LOOH) was examined in cultured human fetal lung fibroblasts, TIG-7. Cyanidin was more effective than pelargonidin or delphinidin in inhibiting LOOH-induced cytotoxicity. The presence of a catechol moiety in the B ring is shown to be important for the protective activities against the cytotoxicity of LOOH.