Androgen withdrawal enhances thymopoeisis as evidenced by increased thymic size, weight, and thymocyte subsets with initial increases in DN and DP and subsequent increases in mature SP populations. Panel A demonstrates that thymic weight increased significantly by 1 week after castration and was maintained for 6 months postoperatively (> 8 mice/group). Panels B-E represent absolute thymocyte counts from 6- to 8-week-old C57BL/6 male mice at various time points after castration or sham castration (6-12 mice per group). (B) Total thymocyte number dramatically rose as well within 1 week after castration and persisted for 3 months before signs of involution. Double-positive (C) and double-negative (D) thymocyte total number were significantly increased by 1 week after castration (P < .005). CD4 (E) and CD8 (F) total thymocyte number rose dramatically by one month (later than the dramatic increase in immature subsets; P < .005).