The muscarinic agonist, cis-2-methyl-4-dimethylaminomethyl-1,3-dioxolane methiodide (CD), and histamine desensitize the responses of guinea-pig ileal longitudinal smooth muscle to subsequently administered CD or histamine, respectively. Desensitization by CD, but not by histamine, was inhibited by concanavalin A (Con A) and this protection was prevented by co-administration of succinyl-Con A or by cytochalasin B or colchicine at concentrations which alone did not affect desensitization. Dansylcadaverine and bacitracin, inhibitors of transglutaminase, both protected against CD desensitization but were without effect on desensitization mediated by histamine. Benzilylcholine mustard, which reduced muscarinic receptor density, significantly reduced CD-induced desensitization. The effects of Con A and the transglutaminase inhibitors suggest that agonist-induced changes in muscarinic receptor distribution or receptor-effector coupling, via cytoskeletal and transglutaminase-sensitive mechanisms, are a component of CD-induced desensitization. These processes do not appear to be involved in histamine receptor-mediated desensitization. Although desensitization by CD or histamine is nonspecific in this preparation, both agonists cross-desensitizing, the effects of Con A, dansylcadaverine and bacitracin clearly indicate differences in the desensitization process elicited by these two stimulants.