Abstract No pro-apoptotic effect of dinitrosyl iron complexes (DNIC) with glutathione, cysteine or thiosulfate was established after incubation of HeLa cells in Eagle’s medium. However, DNIC with thiosulfate manifested pro-apoptotic activity during incubation of HeLa cells in Versene’s solution supplemented with ethylene diamine tetraacetate (EDTA) known to induce the decomposition of these DNIC. The water-soluble о-phenanthroline derivative bathophenanthroline disulfonate (BPDS) had a similar effect on DNIC with glutathione during incubation of HeLa cells in Eagle’s medium. It was assumed that EDTA- or BPDS-induced pro-apoptotic effect of DNIC with thiosulfate or glutathione is coupled with the ability of decomposing DNIC to initiate S-nitrosylation of proteins localized on the surface of HeLa cells. Presumably, the pro-apoptotic effect of S-nitrosoglutathione (GS-NO) on HeLa cells preincubated in Eagle’s medium is mediated by the same mechanism, although the pro-apoptotic effect based on the ability of GS-NO to initiate the release of significant amounts of NO and its oxidation to cytotoxic peroxynitrite in a reaction with superoxide should not be ruled out either. No apoptotic activity was found in the presence of bivalent iron and glutathione favoring the conversion of GS-NO into DNIC with glutathione. It is suggested that interaction of HeLa cells with intact DNIC with glutathione or thiosulfate results in the formation of DNIC bound to cell surface proteins.