The effects of Bombina variegata cutaneous venom (Bvv) on eukaryotic cell growth has been assessed employing the human leukaemic cell line HL 60, by liquid and agar semisolid cultures and 51Cr release assay. HL 60 cells growth is impaired by Bvv in a dose-dependent fashion in both culture systems. The arrest of proliferation requires a contact time lower than 3 min and it is not reversed by washing and culturing the cells in a Bvv-free medium. Similarly, an extremely short exposure time is needed to determine maximum 51Cr release. Neither the agar medium nor the fetal calf serum interact with Bvv effects, which, according to the above findings, must be regarded as cytolytic in nature. In both liquid and the agar-semisolid culture Bvv cytolytic activity half life is about 8 hr. The cytolytic properties of Bvv are thought to be part of the chemical defence system of amphibian skin.