1. The depolarizing effectiveness of azelainylcholine (AzCh, a 7-C-chain dicholine) is about 10 times higher than that of succinylcholine (SCh, a 2-C-chain dicholine) in skeletal muscles of chick, frog and fish, and in body muscles of the earthworm. 2. In the chicken anterior latissimus dorsi (ALD) muscle, AzCh is about 100 times more effective than SCh. 3. In contrast to that in mammalian muscles, the AzCh-SCh sensitivity difference is not increased by denervation in frog muscles. 4. d-Tubocurarine is equally effective in the ALD and in other chicken muscles; its effectiveness is not decreased by denervation in frog muscles. 5. Cells containing muscarinic acetylcholine receptors are weakly sensitive to dicholines or not at all.