It is believed that free fatty acids contribute to the pathogenesis of type 2 diabetes in humans. We have recently shown that lipoapoptosis of human beta-cells is specifically induced by saturated fatty acids while unsaturated had no effect. In the present study we tested the effect of co-incubation of different saturated and unsaturated free fatty acids on lipoapoptosis in beta-cells. RIN1046-38 cells and isolated human beta-cells were incubated with combinations of saturated fatty acids (palmitate, stearate) and mono- or polyunsaturated fatty acids (palmitoleate, oleate, and linoleate). Cells were incubated for 24-72 h with 1 mM fatty acids. All unsaturated fatty acids tested completely prevented palmitate- or stearate-induced apoptosis of rat and human beta-cells as assessed by flow cytometric cell cycle analysis,and TUNEL assay. This might suggest that apoptosis in vivo is predominantly determined by the content of unsaturated fatty acids in a mixed fatty acid pool. (C) 2002 Elsevier Science (USA). All rights reserved.