The influence of three chemotherapeutic agents, acronycine, bleomycin and cytosine arabinoside, alone and combined with radiation, on cell cycle progression and viability of L-cells was examined. The percentages of cells in G1, S and (G2 + M)-phases as derived from pulse cytophotometric DNA distribution patterns were recorded as a function of exposure time. After 24-h treatment with 10 microgram/ml acronycine, 46.4% of cells were accumulated in (G2 + M)-phase compared to 12.1% in the controls. This accumulation was significantly enhanced by an irradiation with 150 rads of X-rays resulting in arresting 63.1% of cells in this phase. Similar findings were obtained after a 24-h treatment with 100 microgram/ml bleomycin. 54.4% of cells were arrested in (G2 + M)-phase by the chemical treatment alone, while the combined treatment, bleomycin and radiation, yielded an accumulation of 66.3% of cells in G2 + M. A 24-h exposure to 0.2 microgram/ml cytosine arabinoside (Ara-C) produced a reversible block of 72.8% of cells in S phase compared to 27.4% in the control cultures. This S block was less pronounced after the combined treatment (51.1%). Some implications of the results for combined therapy are discussed.