The configurational and conformational peculiarities of the cis and trans isomers of decahydroquinoline and decahydro-4-quinolone are discussed, and information on a new class of cis-decahydroquinoline alkaloid-neurotoxins and some data on the effect of the three-dimensional structures of decahydroquinoline derivatives on pharmacological activity are presented. © 1987 Plenum Publishing Corporation.