Various esters of omega-homo-prostaglandin E1 and prostaglandin E1 were prepared in a yield of 28-55% to investigate their effect on ADP-induced aggregation of rat blood platelets. The biopotency of the omega-homo-PGE1-esters is about four times higher than that of the corresponding PGE1-esters. Furthermore, the biopotency of aliphatic esters decreases with increasing chain length of the ester group.