Thirteen patients with vitreous opacities were treated by intravitreal injection of urokinase. The central corneal thickness was measured daily on both eyes. Determination of visual acuity and ophthalmoscopy were done before treatment and at each following attendance (longest period of follow-up was seven months). The central corneal thickness increased after urokinase injection and the maximum thickness was reached on the second day. On the 6th day a secondary rise in corneal thickness occurred. The possible relation to the fibrinolytic system is discussed. There was an effect on the vitreous opacities in 8 out of 13 eyes. Only in 3 of the 13 eyes did visual acuity increase. This relative poor result as regards visual acuity in most cases was due to membranes in the vitreous.