A series of derivatives of the novel cyclopentano[f]- and [h]-1,2,3,4-tetrahydroisoquinolines has been synthesized and screened by hypotensive properties in the unanesthetized DCA hypertensive rat and for acute toxicity in the mouse. Substitutions were made in the parent structures at both the heteroatom and the 5 and 6, and 7 and 8 positions. Bulky lipophilic substitutions on the heteroatom yielded compounds producing moderate depressions in blood pressure over extended periods of time. One member of the series produced a significant hypertensive response. Some heart stimulant properties (unaccompanied by effects on blood pressure) were observed with some compounds. In general, the compounds were relatively toxic. The introduction of the bulky lipophilic groupings on the heterocyclic nitrogen appeared to be associated with a reduction in toxicity.