The antiproliferative activity of several flavonoids isolated from Linaria reflexa Desf. (Scrophulariaceae) was evaluated in vitro by the SRB assay against the large cell lung carcinoma cell line COR-L23, hepatocellular carcinoma cell line HepG-2, renal adenocarcinoma cell line ACHN, amelanotic melanoma cell line C32, colorectal adenocarcinoma cell line Caco-2, and normal human fetal lung MRC5. Chemical modifications, that is acetylation, hydrolysis of rutinose unit, and hydrolysis of the terminal rhamnose unit, were performed on pectolinarin. Pectolinarin exhibited strong cytotoxic activity on COR-L23, Caco-2, and C32 cell lines with an IC50 of 5.03, 6.18, and 7.17 microM. Similar activities were recorded for the three natural monoacetyl pectolinarin derivatives linariin, isolinariin A, and isolinariin B. In contrast, peracetylpectolinarin displayed only marginal activity.