To investigate the role of the acetylcholine receptor (AchR) in the pathogenesis of paraneoplastic Myasthenia gravis (MG), we screened a cDNA library of a MG-associated thymoma with a DNA oligonucleotide coding for aa 371-378, i.e. for part of the very immunogenic cytoplasmatic epitope (VICE-alpha, aa 373-380) of the human AChR alpha-subunit. We isolated two cDNA clones. Analysis of these clones has identified an open reading frame of 1371 bp, coding for the AChR alpha-subunit. No point mutation, insertion or deletion could be detected. Since the thymoma did not contain thymic myoid cells, which normally express AChR, the origin of the AChR transcripts must be the tumor cells itself. These findings confirm former results, where AChR alpha-subunit sequences from MG-thymomas were amplified by PCR.