OBJECTIVE Microdialysis has been used in eye research for almost a decade. We have previously developed and used it mainly for chronic experiments and here it is used in acute experiments. It is highly suitable for both administration and withdrawal of substances from the eye, as it only permits molecules to cross the intraocular membrane without any net fluid movement in or out of the eye. METHODS We have here investigated the ability of 125I labeled NGF (nerve growth factor) to cross a previously implanted high permeability membrane of a new type (polyether sulphone, PES, cutoff at 100000 daltons) in the rabbit vitreous. It was perfused for different time periods with a solution containing NGF The radioactivity of the entire vitreous was then counted. RESULTS The results show detectable levels (up to 10(-11)M) of the substance after the perfusions. CONCLUSIONS We conclude that microdialysis with PES membranes is a possible method for the intraocular administration of NGF.