Objective: To explore the possible mechanisms of growth regression of human androgen dependent prostate carcinoma cells caused by androgen withdrawal. Methods: After 24 h of treatment with 1 × 10-9 mol/L dihydrotestosterone (DHT), the expression of phosphorylated ERK proteins and cell cycle regulation molecules including CDK2, CDK4, CDK6 and P27kip1 in human androgen dependent prostate carcinoma cell line LNCaP was measured by Western blot analysis 0 h, 8 h and 24 h of after androgen withdrawal. Human androgen independent prostate carcinoma cell line PC-3 was also examined as control. Results: Down-regulation of phosphorylated ERK, CDK2, CDK4 and CDK6 and up-regulation of P27kip1 were found initially in LNCaP cell line 8 h after androgen withdrawal. The levels of phosphorylated ERK and CDKs decreased continuously and reached the lowest after 24 h, while continuous elevation of P27kip1 was detected thereafter to 24 h. No expression change of phosphorylated ERK, CDKs and P27kip1 were detected in PC-3 cel Objective: To explore the possible mechanisms of growth regression of human androgen dependent prostate carcinoma cells caused by androgen withdrawal. Methods: After 24 h of treatment with 1 × 10-9 mol / L dihydrotestosterone (DHT), the expression of phosphorylated ERK proteins and Cell cycle regulation molecules including CDK2, CDK4, CDK6 and P27kip1 in human androgen dependent prostate carcinoma cell line LNCaP were measured by Western blot analysis 0 h, 8 h and 24 h of after androgen withdrawal. Human androgen independent prostate carcinoma cell line PC-3 Results: Down-regulation of phosphorylated ERK, CDK2, CDK4 and CDK6 and up-regulation of P27kip1 were found initially in LNCaP cell line for 8 h after androgen withdrawal. The levels of phosphorylated ERK and CDKs decreased continuously and reached the lowest after 24 h, while continuous elevation of P27kip1 was detected thereafter to 24 h. No expression change of phosphorylated ERK, CDKs and P27kip1 were de tected in PC-3 cel