We have previously reported the existence of 2 forms of mRNA for the human muscle acetylcholine receptor (AChR) alpha-subunit, thought to be generated by alternate splicing of a primary transcript and to encode 2 alpha-subunit protein isoforms. The 2 predicted alpha-subunit isoforms, differing by the insertion of 25 amino acids at position 58/59, have been synthesized from cRNA transcripts using rabbit reticulocyte lysates; these protein isoforms could be differentiated by immunoprecipitation using antibodies raised against synthetic peptides. The antibodies were used to demonstrate translation of both AChR alpha-subunit isoforms in the rhabdomyosarcoma (muscle) cell line TE671, in an approximate 1:1 ratio.