The type of DNA damage and the role of poly (ADP-ribosyl) polymerase (ADPRP) and sulphated glyprotein 2 (SGP-2) in programmed cell death (apoptosis) was investigated in the following model systems: i) rat thymocytes treated with dexamethasone (DEX) eitherin vitro orin vivo; ii) human perypheral blood mononuclear cells (hPBMCs) exposed to oxygen free radicals (OR); iii) K562 cell line killed by hPBCs during spontaneous (NK) or interleukin-2 (IL-2)-induced (LAK) cytotoxic activity. The results suggest that ADPRP and SGP-2 are involved in the apoptotic process, but their role probably differs according to the type of cell and the inducing damage/stimulus. Moreover, no simple correlation appears to exist between the extent of DNA damage and cell survival or cell death.