The regulation of genes for acetylcholine receptor (AChR), myogenic factors and other muscle-specific proteins has been analyzed in experimental autoimmune myasthenia gravis (EAMG) and following denervation. The levels of the transcripts for the myogenic factors, MyoD1, myogenin and MRF4, were measured using Northern blot analysis. Myogenin and MRF4 transcript levels were observed to be 3.1- and 2.6-fold higher in muscle of rats with EAMG than in controls, respectively. MyoD1 levels, however, remained unchanged. The increases in AChR, myogenin and MRF4 mRNAs were one order of magnitude higher in 2-week denervated muscle than in the myasthenic muscle. The levels of muscle creatine kinase (MCK), alpha-actin and muscle dystrophin transcripts were also analyzed. Dystrophin levels were found to be 1.7- and 4.7-fold higher in EAMG and denervated muscle, respectively, than in controls; in contrast, MCK and alpha-actin levels remained unchanged.