Prostaglandin F 2 α analogues have recently been introduced on the market for glaucoma treatment. While these drugs have a well-documented intraocular pressure reducing effect only a limited number of studies have been published regarding their effects on the microvasculature in the eye. Since many naturally occurring prostaglandins have marked effects on the cardiovascular system it is conceivable that synthetic prostaglandins used as glaucoma drugs may exert microvascular effects in the eye, even if they exhibit receptor selectivity. Latanoprost, the active principle of Xalatan ( R) eye drops, is a selective FP prostanoid receptor agonist, and much of the paper is focused on the microvascular effects of latanoprost and some closely related prostaglandin analogues. The purpose of the paper is to review the literature on the microvascular effects of prostaglandins in the eye, and to present some unpublished data on the effects of selective prostaglandin analogues. Most of the prostaglandin analogues studied exhibit selectivity for the FP prostanoid receptor.Results from studies with the following prostaglandin analogues are presented in the paper: PGF 2 α -isopropyl ester (PGF 2 α -IE), 17-phenyl-18,19,20-trinor-PGF 2 α -isopropyl ester (17-phenyl-PGF 2 a -IE), 15-keto-17-phenyl-18,19,20-trinor-PGF 2 α -isopropyl ester (15-keto-17-phenyl-PGF 2 a -IE), 13,14-dihydro-17-phenyl-18,19,20-trinor-PGF 2 α -isopropyl ester (latanoprost), 13,14-dihydro-15R,S-17-phenyl-18,19,20-trinor-PGF 2 α -isopropyl ester (PhXA34), 17-phenyl-18,19,20-trinor-PGE 2 -isopropyl ester (17-phenyl-PGE 2 -IE), and 19R-hydroxy-PGE 2 (19R-OH-PGE 2 ). The regional blood flow has been determined with radioactively labelled microspheres, the blood volume with 5 1 Cr labelled erythrocytes and the capillary permeability to albumin with 1 2 5 I and 1 3 1 I labelled albumin.PGF 2 α -IE has been shown to exert marked microvascular effects in the rabbit anterior segment including vasodilatation, increased capillary permeability, and a breakdown of the blood-aqueous barrier. 17-phenyl-PGF 2 α -IE, 15-keto-17-phenyl-PGF 2 α -IE, and PhXA34/latanoprost exerted significantly less vasodilatory effect, and little effect on capillary permeability was seen with the FP receptor agonists when studied with Evans blue. Intravenous administration of PhXA34 at a dose range of 1-100<space>μg/kg b.w. had no consistent effect on the regional blood flow in the eye indicating that FP receptors in the ocular blood vessels are not expressed in the rabbit, or alternatively are not functionally coupled to regulation of vascular tone.In cats topical application of PGF 2 α -IE had no significant effect the on the regional blood flow in cannulated eyes. No blood flow experiments were performed in intact eyes with PGF 2 α -IE. 17-phenyl-PGF 2 α -IE and latanoprost caused some vasodilation in the anterior segment. None of the analogues had any significant effect on the blood volume in the ocular tissues, but an increase in capillary permeability to albumin was seen in several tissues of the eye. However, in the eyelid, nictitating membrane and conjunctiva exposed to high concentrations of the prostaglandins no or only little leakage of albumin was detected. It appears that the intraocular microvasculature in the cat exhibits some sensitivity to FP prostanoid receptor agonists.In the cynomolgus monkey eye PGF 2 α -IE has been shown to cause a dramatic increase in blood flow of the anterior uvea, but only weak effect was detected with the selective FP receptor agonists and an EP 1 receptor agonist after topical administration. Intravenous infusion of latanoprost at a dose range of 0.6-6<space>μg/kg b.w. had little effect on the blood flow in most ocular tissues, and the same was true for 17-phenyl-PGE 2 , a relatively selective EP 1 receptor agonist, after intracardiac infusion at about the same dose range. Intravenous infusion of the EP 2 receptor agonist 19R-OH-PGE 2 markedly reduced the vascular resistance in the eye. No significant effect was seen on the blood volume in the ocular tissues with any of the FP receptor agonists after topical administration. PGF 2 α -IE increased the capillary permeability to albumin in the anterior segment and possibly the retina, but 17-phenyl-PGF 2 α -IE and latanoprost/ PhXA34 had no effect on capillary permeability in any of the ocular tissues.Based on the results of previous studies and the experiments described in the present paper it is evident that PGF 2 α has significant microvascular effects in the rabbit, cat and monkey eye, causing vasodilation and/or increased capillary permeability, whereas selective FP receptor agonists such as latanoprost exert no or minimal effects in the primate eye, and markedly reduced microvascular effects in the rabbit eye. However, little difference between PGF 2 α and the selective FP receptor agonists was seen in the cat eyes. It also appears that the EP 1 receptor like the FP receptor is not involved in the regulation of vascular tone in the primate eye, whereas stimulation of the EP 2 receptor reduces the vascular resistance in the monkey eye. Finally, the microvascular parameters in the control eyes of cats and monkeys are compared and discussed.