The thymidine analogs, IdU and CldU, are not as sensitive as BrdU. Overall, BrdU-labeled cells in the dentate gyrus were more abundant than either IdU- or CldU-labeled cells (** P < 0.05) suggesting that these thymidine analogs are not labeling cells undergoing S-phase with equal probability. Also, BrdU antibodies did not label IdU or CldU with specificity. Although BD detected more IdU-labeled cells than Accurate, some IdU-positive cells were found with the Accurate antibody. In addition, both BD and Accurate detected a substantial number of CldU-labeled cells. Bars represent mean ± SEM, * P < 0.05.