Besides anabolic steroids, the most common performance-enhancing hormones are erythropoietin (EPO), insulin, GH, and gonadotropins, mostly indistinguishable from endogenous hormones and with very short half-life. This makes virtually impossible to demonstrate their use by measuring their concentration in the blood or urine. A possible approach to the problem may lie in in-direct demonstration through detection of the biological effects of these substances. The finding of an increased hematocrit level is suspicious but not clearly demonstrative of EPO abuse. Very high levels of circulating EPO could be associated with a strong suspicion of doping, when associated to other abnormal parameters, such as Ht, sTFRr, EPO, RDW. The presence of antibodies against the polysaccharide fraction of lateral chains of EPO has been observed only in patients treated with rhEPO. Owing to the pulsatile pattern of GH, particularly during physical exercise, pathologically high values may be found in normal subjects. Therefore, as in the case of EPO, evidence of GH abuse can be gathered only indirectly by detecting the biological effects of its administration. In training subjects GH treatment increased GH, IGF-I, IGFBP-3 and ALS, and decreased IGBP-2. After cessation of treatment IGF-I, IGFBP-3 and ALS approached basal values between 49 and 96 h. Also the bone parameters PICP ICIP, PIUP and osteocalcin increased significantly. Four days after cessation of treatment, levels of PIIIP and ICTP were still abnormally elevated. In conclusion, increases in IGF-I, IGFBP-3, ALS, PIIIP and ICTP are all indicative of recent GH abuse or of acromegaly.