Antibodies to synthetic peptide (125-148) of the alpha-subunit of human nicotinic acetylcholine receptor in sera from patients with myasthenia gravis. We measured the amount of antibodies to a synthetic peptide that corresponds to the alpha-subunit residues Lys125-Thr148 of human acetylcholine receptor (AChR) in myasthenic sera. We detected anti-peptide antibodies in 52% (89/171) of the patients with myasthenia gravis (MG), but none in any of the healthy controls. Anti-peptide antibodies should provide a valuable immunologic parameter for the clinical evaluation of MG, but no apparent correlation was observed between the titers of anti-peptide and anti-AChR antibodies. 