In an open label, single dose study on ten glaucoma patients with bilateral untreated IOP levels exceeding 30 mmHg the effects of 100 micrograms human atrial natriuretic factor (HANF) on IOP, systolic blood pressure, pulse rate and serum electrolytes were investigated. The intravenous application of HANF decreased IOP over more than 8 hrs. The magnitude of IOP reduction in this study was in the range of 4-7 mmHg. There was no significant change in blood pressure, pulse rate or serum electrolytes. The verified, yet still limited efficacy of HANF on IOP in glaucoma warrants further investigations.