An array of 55 flavones having a variety of substituents was evaluated for cytotoxicity in five cancer cell cultures: A-549 lung carcinoma, MCF-7 breast carcinoma, HT-29 colon adenocarcinoma, SKMEL-5 melanoma, and MLM melanoma. Fifteen of the 55 flavone derivatives were significantly active against at least one of these cell cultures, and 4'-[(t-butyldi-methylsily)oxy]-7,8-dihydroxy-3',5'- dimethoxyflavone [40] was the most active of all. Structure-activity relationships of these compounds are discussed.