At the inception of this study, 6-hydroxydopamine (6-HD) was administered to 137 eyes of 100 glaucoma patients by subconjunctival injection (27 applications) and later by iontophoresis (202 applications). Eighty-four patients were receiving maximum medical therapy, and 24 had had previous glaucoma surgery. Seventy-seven had primary open-angle glaucoma. In 49 patients with data adequate for analysis, 6-HD therapy was effective in 41%, questionable in 31%, and not effective in 28%. The median peak-pressure drop was 13 mm Hg from a baseline of 26 by subconjunctival injection and 6 mm Hg from a baseline of 24 by iontophoresis. The median effective period before return to baseline pressure was 2.5 months. There was a direct correlation between the effectiveness of epinephrine therapy with and without 6-HD. Iontophoresis is a much more practical method for the administration of 6-HD.