The use of affinity chromatography on wheat germ agglutinin columns to partially purify detergent extracts of muscarinic acetylcholine receptor from porcine atria is described. The procedure results in a 20-fold purification of the protein. The partially purified protein binds [3H]L-QNB (the L isomer of quinuclidinyl benzilate) with an observed association rate constant 2- to 3-fold lower than that found for the detergent extract; however, incubation with column fractions eluted prior to the receptor gives an association rate constant similar to that for detergent extracts. The component responsible for this effect is nondialyzable and protease sensitive, indicating that it may be a protein or high-molecular-weight peptide. Affinity labeling experiments with [3H]propylbenzilylcholine mustard [N. J. M. Birdsall, A. S. V. Burgen, and E. C. Hulme (1979) Brit. J. Pharmacol. 66, 337-342] show radioactivity incorporated mainly in a broad peak of apparent molecular weight 75,000 +/- 5000.