Addition of ascorbate (8 or 16 mM) resulted in an increase in H2O2 formation in all of the cancer cell lines (SF268, OVCAR-8, LOX IMVI, K562, NCI-H226, HT29, DU-145, HS-578T, SN12C) independent of the tumour type; as expected, the addition of 100 μg/ml catalase completely destroyed the ascorbate-induced H2O2 in all nine cell lines (Fig. 1B). The gene discussed is CAT; the disease is cancer.