Vitamin C has been suggested^1,2 and disputed³ as an anti-cancer agent. For cells in culture, no preferential effect against any type of cancer has yet been demonstrated. Our aim here is to show that vitamin C is selectively toxic to at least one type of malignant cell—a melanoma—at concentrations that might be attained in humans. Copper ions react with ascorbate and generate free radicals in solution⁴. Ascorbate when combined with copper rapidly reduces the viscosity of DN A solutions and has exhibited some carcinostatic effects on transplanted sarcoma 180 tumours in mice⁵. We reasoned that the elevated copper concentration in melanoma^6,7 could result in a more selective toxicity for ascorbate.