A novel series of prostaglandin F (PGF) analogues have been prepared and evaluated in vivo and in vitro. Their intraocular pressure (IOP) lowering effects and potential side-effects, as prodrug eye drops, have been tested in cats, monkeys and rabbits. Furthermore, the PGF-analogues were tested as free acids for FP-receptor agonistic activity on cat iris sphincter. The results were compared to that of PGF2 alpha (C#1). Based on the structure-activity relationship investigations, inversion of the configuration, at carbon-9 (C#3) or carbon-11 (C#4), changes the potency and the receptor profile of PGF2 alpha. Replacement part of the omega-chain of PGF2 alpha with a benzene ring changes the potency and receptor profile of PGF2 alpha. The optimal position of the benzene ring is on carbon-17, 17-phenyl-18,19,20-trinor PGF2 alpha-isopropyl ester (C#8), and exhibited a much higher therapeutic index in the eye than PGF2 alpha or its ester. The biological activity of different substituents on the C#8 benzene ring have also been studied. Interestingly, introduction of a methyl group at positions 2 or 3 of the benzene ring (C#16 or C#17) affords compounds which are biologically more active than the methyl group at the 4-position (C#18). Furthermore, one of the analogues 13,14-dihydro-17-phenyl-18,19,20-trinor PGF2 alpha-isopropyl ester (latanoprost), has been found in clinical studies to be a highly potent and efficacious IOP-reducing agent for the treatment of glaucoma.