Background: Significant progress in treatment of metastatic castration resistant prostate cancer (mCRPC) has been made. Biomarkers to tailor therapy are scarce. To facilitate decision-making we evaluated dynamic changes of alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and prostate specific antigen (PSA) under Abiraterone acetate (AA). ALP-Bouncing can be observed during very early AA-therapy. Methods: Men with bone mCRPC (bmCRPC) on AA 12/2009-01/2014 were analyzed. Dynamic ALP-, LDH- and PSA-changes were analyzed as predictors of best clinical benefit (BCB) and overall survival (OS) with logistic-regression, Cox-regression and Kaplan-Meier-analysis. Results: 39 pre- and 45 post-chemotherapy patients with median follow up of 14.0 months were analyzed. In univariate analysis failure of PSA-reduction ≥50% (PSA-red≥50%) and failure of ALP-Bouncing were the strongest predictors of progressive disease (p=0.003 and 0.021). Rising ALP at 12 weeks (ALP12), no PSA-red≥50% and no ALP-Bouncing were strongest predictors of poor OS, (all p<0.001). Kaplan-Meier-analysis showed worse OS for ALP12, no PSA-red≥50% and no ALP-Bouncing (p<0.001). In subgroup-analysis of oligosymptomatic patients all parameters remained significant predictors of poor OS, no PSA-red≥50% and ALP12 being the strongest (p<0.001). In multivariate analysis PSA-red≥50% remained independent predictor of OS for the whole cohort and for the oligosymptomatic subgroup (p=0.014). No patient with ALP-Bouncing had PD for BCB. Patients with ALP12 had no further benefit of AA. Conclusions: Dynamic changes of ALP, LDH and PSA during AA-therapy are associated with BCB and OS in bmCRPC. ALP-Bouncing occurring earlier than PSA-changes and rising ALP12 under AA may help to decide whether to discontinue AA.