Abstract A new series of substituted 2, 7-diazaspiro [3.5] nonan-1-ones (1a-I), structurally related to the muscarinic agonist RS-86, has been synthesized and tested for cholinergic properties both in vitro and in vivo. None of the compounds showed significant cholinergic properties at either the central or peripheral level. A possible explanation for the lack of activity is given.