The influence of topically applied clonidine 0.125% on ocular hemodynamics was investigated in ten patients with open-angle glaucoma and ten healthy volunteers, using a new, differentiated method. Ocular perfusion pressures were determined by Ulrich's method of oculo-oscillodynamography. Following monocular application of clonidine 0.125% eye drops a clear decrease in systemic blood pressure and a somewhat less pronounced reduction of ocular perfusion pressure was observed in both groups of patients. The reduction in ocular perfusion pressures was higher in the eye after drop application than in the untreated control eye. It must therefore be assumed that clonidine 0.125% eye drops have a local perfusion pressure-reducing effect in addition to their systemic effect.