In the insect Lymantria dispar cell line IPLB-LdFB the presence of a Bcl-2-like molecule has been demonstrated. The Western blot analysis performed on the cells incubated with 2-deoxy-D-ribose (dRib), an apoptotic inducer, revealed that, in comparison with the control, the Bcl-2 expression was unaffected. Furthermore, incubation of the insect cells with an anti-Bcl-2 polyclonal antibody inhibited the apoptotic effect induced by dRib, and provoked mitochondrial membrane depolarization without any apoptotic phenomena. Similar behaviour was observed using the K+ ionophore valinomycin. From these findings, we hypothesize that the L. dispar Bcl-2-like protein is essential for maintenance of the mitochondrial membrane potential, but not, as usually thought, for the regulation of programmed cell death.