The effect of hydroxyurea (HU) on cell growth, cell cycle progression, and the intracellular accumulation of 2',3'-dideoxycytidine (ddC) and ddCTP formation was examined. Twenty-four-hour exposure of H9 cells (human lymphocytic cell line) to 500 microM HU significantly increased the cells in the G1 phase and inhibited cell growth to 33.3 +/- 10.6% of control. The total intracellular ddC and ddCTP accumulation in HU-treated cells increased to 232.3% and 310% of control, respectively.