Cis- and trans-1,2-Cyclobutanediamines bearing appropriate N-methyl and N-acyl substituents were prepared as analogues of diethylcarbamazine (DEC). None displayed activity against Litomosoides carinii in the gerbil despite substantial structural and stereochemical similarities to the parent drug. The inactivity of these drugs is rationalized in terms of eclipsed pharmacophore configurations and the increased population of unfavorable rotational conformations made possible by the exocyclic position of both pharmacophores. To provide perspective for these conclusions, the literature on DEC analogues is briefly summarized and structure-activity data are discussed in terms of critical structural factors associated with microfilaricidal activity. Generalizations on structural principles governing activity are advanced which encompass test results for the large majority of DEC analogues.