Induction of apoptosis assessed by fluorescence microscopy in MON cells following:A) irradiation with X-rays at doses of 1 (X1), 2 (X2), 4 (X4) or 8 Gy (X8), or continuous exposure to wortmannin at 0.5 (W0.5), 1 (W1), 2 (W2) or 4 μM (W4), or combined treatments with 1 Gy X-rays plus 0.5 μM wortmannin (X1+W0.5), 2 Gy X-rays plus 1 μM wortmannin (X2+W1), 4 Gy X-rays plus 2 μM wortmannin (X4+W2) and 8 Gy X-rays plus 4 μM wortmannin (X8+W4).B) continuous exposure to vinblastine at 1 (V1), 2 (V2), 4 (V4) or 8 nM (V8), or to wortmannin at 0.5 (W0.5), 1 (W1), 2 (W2) or 4 μM (W4) or to the associations 1 nM vinblastine plus 0.5 μM wortmannin (V1+W0.5), 2 nM vinblastine plus 1 μM wortmannin (V2+W1), 4 nM vinblastine plus 2 μM wortmannin (V4+W2) and 8 nM vinblastine plus 4 μM wortmannin (V8+W4). Cells, cultured and treated in Petriperm dishes, were stained with Hoechst 33342 and visualized with an inverted epifluorescence microscope 24 h after the beginning of the treatments. Fragmented, marginated chromatin defined apoptotic cells. Quantitative analyses were performed by counting at least 1000 cells for each treatment. Data in each graph represent the means values ± standard deviations of two experiments.