We have studied the mRNAs encoding all four subunits of the acetylcholine receptor in 13-day embryonic, innervated and denervated chicken pectoral muscle. In all three states the transcript sizes of the alpha, beta-, gamma- and delta-subunit mRNAs were approximately 3.2, 2.8, 1.8 and 1.9 kb respectively. Denervation was found to result in a large increase in the steady-state levels of each mRNA compared with those in innervated muscle. This increase was 8- to 9-fold for the beta and delta subunits and approximately 12-fold for the alpha subunit. The evidence obtained shows a coordinate regulation of the acetylcholine receptor genes in response to denervation. Interestingly, no gamma-subunit transcript was detected in innervated muscle, while significant levels were detected in embryonic and denervated tissue. This evidence suggests that there exists in a non-mammalian muscle acetylcholine receptor an additional subunit, analogous to the bovine epsilon subunit, and shows that the extra-junctional receptor of adult denervated muscle is produced by the same set of mRNAs which produce the major form of the receptor in embryonic muscle.