Twenty-four rats, trained to discriminate 1.0 mg/kg of (+/-)-DOM, i.e. (+/-)-2,5-dimethoxy-4-methylphenylisopropylamine, from saline under a VI-15 schedule of reinforcement, were challenged with a series of DOM homologs. The agents examined included the 4-ethyl (DOET), -propyl (DOPR), -butyl (DOBU), -tertiary butyl (DOTB) and -amyl (DOAM) derivatives as well as the R(-)- and S(+)-isomers of DOET. The (+/-)-DOM stimulus was found to generalize to all of the agents, except DOTB and DOAM, where only partial generalization occurred. The results suggest that the stimulus properties produced by the latter two compounds may differ from those of the remainder of the series. Furthermore, the ED50 values obtained, for those compounds to which the DOM-stimulus generalized, correlated significantly (r2 = 0.94) with the human hallucinogenic potencies of these agents.