The effect of aurintricarboxylic acid (ATA) on cell growth and proliferative capacity was studied in human ovarian SKOV3 and breast MCF7 carcinoma cells. ATA moderately inhibited cell growth measured by a Neutral red assay after a 24-hour incubation of the cells in the presence of ATA. The ATA-treated cells displayed a markedly decreased capacity to proliferate, as was evident from a colony formation assay. The initial and delayed anti-proliferative effects of ATA were dose-dependent. Together, the results indicated that ATA offers the potential of being recognized as an anti-tumor drug, at least in certain types of cancers.