As part of our program directed toward the development of new, selective agents with potential utility in the treatment of urinary incontinence associated with bladder muscle instability, a series of 4-(1-imidazolyl)-2,2-diphenylbutanamide derivatives was prepared. These compounds were examined for M₁, M₂, and M₃ muscarinic receptor subtype selectivity in isolated tissue assays. The compounds that showed potency and/or selectivity in these tests were further evaluated for in vivo antimuscarinic effects on various organs and tissues, including urinary bladder, salivary gland, and eye in rats. The structure-activity relationships of 4-(1-imidazolyl)-2,2-diphenylbutanamide derivatives and related compounds are also discussed. This study led to the identification of a novel dual antagonist of M₁ and M₃ muscarinic receptors, 4-(2-methyl-1-imidazolyl)-2,2- diphenylbutanamide (KRP-197/ONO-8025), as a candidate drug for the treatment of urinary bladder dysfunction.