Effect of cytotoxic drugs in combination with hydralazine and valproic acid in HeLa cells. HeLa cells were treated for 24 hours with cisplatin, adriamycin or gemcitabine at or close to IC50 plus hydralazine and valproic acid. Afterwards medium was removed and fresh medium containing only hydralazine and valproic acid was added for additional 48 hours after which viability was measured. There was a statistically significant higher cytotoxicity of the chemotherapeutic agent when used in combination with hydralazine plus valproic acid. Viability with cisplatin was 37% and zero after co-treatment with hydralazine-valproic acid (p < 0.002). Corresponding values for adriamycin and gemcitabine alone or with co-treatment were 42% versus 27% (p < 0.020) and 45% versus 37% (p < 0.012) respectively.