PC-3 human prostate carcinoma cells were treated with 100 mg/ml 1-methyl-ascorbigen (Me-Asc). This treatment resulted in a significant decrease in tumor cell number in parallel with an increase in apoptotic cells. The formaldehyde (HCHO) level in the culture medium was also increased. Dimedone (Di), a known capture molecule forming formal-demethone with HCHO, applied simultaneously with Me-Asc in 10 mg/ml doses diminished the apoptosis-inducing effect of Me-Asc. The possible role of in situ generated HCHO in the induction of apoptosis is discussed.