Duration of the mitotic cycle in root-tip meristems of Brassica juncea was determined following autoradiographic studies with tritiated thymidine and standard cell cycle analysis techniques. Mitotic cycle time was estimated as 12 hours, of which the distribution of component phases was: G1, 2.7 hours; S, 5.5 hours; G2, 3.5 hours; and M, 0.284 hours, respectively. The onset of S in the seeds commenced 13 hours after soaking in labeled thymidine. Among the component phases of M, metaphase duration was the longest, followed by prophase. The results suggest the possibility that mitotically selected cells with significantly better synchrony of entry in S could be obtained within 15 hours of treatment with hydroxyurea in the seeds.