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Six aglycone flavonoids and their corresponding glycosides: genistein and genistin, quercetin and rutin, apigenin and apigenin 7-O-β-D-(6-p-coumaroyl) glucoside, as well as the aglycone daidzein isolated from Astragalus verrucosusMoris, were tested for their apoptosis-inducing potential. In vitrotechniques that monitor bioactivity through morphological and biochemical changes were carried out on HCT116 (human colon carcinoma) and MCF7 (human Caucasian breast adenocarcinoma) cancer cell lines. Dose-dependent cytotoxic effects were monitored through changes in mitochondrial dehydrogenase activity using the standard MTT assay. The median inhibitory concentration (GI50) determined from the dose-response curves showed that the aglycones apigenin and quercetin were the most bioactive (low GI50), whilst daidzein and genistein, which had not been previously tested on these cell lines, showed a smaller cytotoxic effect (high GI50). The remaining flavonoids, mostly glycosides, showed negligible cytotoxicity. Morphological changes were monitored by microscopic observation with a photographic record. Results showed important hallmarks of apoptosis, including cell rounding with reduction of cell volume, small condensed nuclei, membrane blebbing and formation of apoptotic bodies.