As part of our interest in the cytotoxic activity of plant extracts, we have studied the whole plant of G. microcephala. We report here the isolation of two isomeric 3-methylated flavonols, namely, 3,3'-dimethylquercetin (5,7,4'-trihydroxy-3,3'dimethoxyflavone) and 3,7dimethylquercetin (5,3',4'-trihydroxy-3,7dimethoxyflavone), following biassay-directed fractionation of a MeOH extract of the plant material. Both compounds were identified by interpretation of their spectral properties (uv with standard testing reagents, ¹H nmr, and ms) and by comparison with literature data (21). They showed cytotoxic activity against P-388 cells in vitro; the ED₅₀'s were 1.7 μg/ml and 3.2 μg/ml for 3,3'-dimethylquercetin and 3,7-dimethylquercetin, respectively. Neither of these flavonols has been obtained from Gutierrezia spp. previously.