The ocular effects of topical prostaglandin F2 alpha (PGF2α) were studied in normotensive human eyes. PGF2α as tromethamine salt, 100 μg, was applied to one eye of 23 normotensive subjects, intraocular pressure (IOP) and pupil size were measured, objective and subjective findings recorded during the first 24 h. Tonography was performed in 10 subjects. As compared with the baseline, PGF2α caused a significant IOP reduction between 1 and 24 h (p < 0.001), being maximal (4.9 ± 0.5 mm Hg, mean ± SEM, p < 0.001) between 4 and 8 h. As compared with the contralateral control eyes, which received 50 μl of saline, treated eyes exhibited significant IOP reduction between 1 and 24 h (p < 0.001), being maximal (4.2 ± 0.4 mm Hg, mean ± SEM, p < 0.001) at 4 h. PGF2α caused marked conjunctival hyperemia in all eyes. Pupillary diameter was not altered. Aqueous flare and cellular response were not seen. Half of the subjects complained of ocular smarting, mild ocular pain or headache. Total outflow facility did not change (p > 0.05). © 1996 S. Karger AG, Basel.