Myostatin propeptide (MYOPRO) and follistatin (FOLLI) are potent myostatin inhibitors. In this study we analysed long-term training effects and effects of androgens on MYOPRO and FOLLI concentrations in blood and skeletal muscle using highly sensitive Immuno PCR. To study training effects in humans young healthy males did either a 3-month endurance-training or a strength-training. Blood and biopsy samples were analysed. Our data revealed that training did not significantly affect MYOPRO and FOLLI concentrations in serum and muscle. To investigate whether total skeletal muscle mass may affect circulating MYOPRO and FOLLI levels, blood samples of tetraplegic patients, untrained volunteers and bodybuilders were analysed. Interestingly, serum levels of MYOPRO were significantly increased in the bodybuilder group. To investigate the effects of androgens on MYPRO and FOLLI levels, orchiectomised rats were treated with testosterone. Myopro was increased in blood and muscle. Immuno PCR analysis demonstrates that moderate training does not affect the concentrations of MYOPRO to FOLLI. However Myopro was significantly increased in serum of bodybuilders. Our observation that androgen treatment results in a significant increase of MYOPRO in the skeletal muscle and serum of rat, provides insights into the molecular mechanisms of anabolic activity of androgens and evidence that this effect may be due to the abuse of anabolic steroids. This observation provides. In addition it could serve as a basis for a test system to detect abuse of myostatin inhibitors.