Synthetic progestagens like melengestrol acetate (MGA) are widely used for oestrus synchronization and for growth promotion in cattle production. The metabolic effects exceed its primary potency as a progestagen. It is speculated thatMGA stimulates follicle development and thereby endogenous oestrogen production, but inhibits ovulation. To investigate the dose-dependent effects on mRNA expression levels, six heifers were fed for 8 weeks with different levels of MGA (0.5, 1.5, 5 mg) daily and two heifers served as controls. The expression of steroid receptor mRNA [androgen receptor (AR), progesterone receptor (PR), oestrogen receptor (ER) ERa and ERb], insulinlike growth factor-1 (IGF-1) and its receptor were quantified in liver, neck (m. splenius) and shoulder muscularity (m. deltoideus). Plasma concentrations of IGF-1 were quantified by radioimmunoassay. In treated animals the MGA plasma levels were elevated over the complete treatment period, corresponding to the MGA treatment concentrations. IGF-1 concentrations of control animalswere at constant levels. Plasma levels for oestradiol (E2) and IGF-1 were increased in the low MGA treatment group. OverdosedMGAdecreased progesterone (P4) and E2 levels. To quantify the IGF-1 and all receptor mRNA transcripts, sensitive and reliable real-time reverse transcription–polymerase chain reaction (RT–PCR) quantification methods were developed and validated in the LightCycler. A dose-dependent relationship between increasing MGA concentration andmRNA expression was observed in liver for AR and IGF-1 receptor, and in neckmuscularity for IGF-1. ERa in liver and neck muscle showed a trend of increasing expression.