Proliferative vitreoretinopathy (PVR) is characterized by cellular proliferation and the formation of intravitreal and periretinal membranes predisposing to traction retinal detachment. Recently, fibronectin, a high-molecular glycoprotein, has been attributed an important role in the pathogenesis of PVR. In order to evaluate the significance of fibronectin as a diagnostic order prognostic marker for PVR, we determined levels of immunoreactive fibronectin in 59 human vitreous specimens by a noncompetitive ELISA technique. Before this study, fibronectin levels in the vitreous had not been investigated taking both protein and iron levels into consideration. The vitreous was obtained during vitrectomies performed for a broad spectrum of vitreoretinal disorders. Our measurements suggest that the amount of intravitreal fibronectin may be correlated with the severity of a manifested disorder rather than being diagnostic for PVR. As long as plasma-derived fibronectin cannot be differentiated from other tissue fibronectins, however, the concentration of this glycoprotein is not a reliable indicator of intraocular proliferative activity. The values for all three parameters--fibronectin, protein, and iron--were significantly higher in revitrectomy samples compared to patients undergoing a first vitrectomy. A somewhat surprising result was a high level of fibronectin in the vitreous of two patients with macular pucker.