A number of carbacyclins having bicyclic substituents on the omega-chain have been synthesized and tested for antiplatelet aggregation activity in vitro (against collagen-induced aggregation of rat platelet), for reduction of systemic blood pressure in vivo (ability to reduce the blood pressure in anesthetized rat by iv injection), and for cytoprotective activity (protection against ethanol-induced rat gastric lesion). The most effective compound for each activity was [3aS-[2E,3a alpha,4 alpha (3R),5 beta,6a alpha]]-5-[hexahydro-5- hydroxy-4-[3-hydroxy-3-(2-indanyl)-1-propynyl]-2(1H)-pentalenylidene+ ++] pentanoic acid (compound 11a), while some 1,4-benzodioxan analogues had selectivity for organ-protective activity, and indan analogues showed selectivity in their antiaggregation activity.