The use of 0.25 and 0.125% echothiophate iodide (Phospholine Iodide) in the management of open-angle glaucoma has been widely accepted. Its use has been confined to those patients in whom the more conventional medical therapy has failed. Initial local side effects, sometimes quite severe, have been an unpleasant feature with this drug, but in many patients these settle after a week or two. Echothiophate iodide 0.06% has recently been introduced in an endeavor to cut down on the unpleasant side effects. Reports of the efficacy of this medication have appeared,1-3 and the suggestion was made that even this low concentration of echothiophate iodide is more effective in maintaining the intraocular pressures on a diurnal basis (round the clock) than the more frequent instillation of pilocarpine.1 The present study was concerned with a comparison of the diurnal pressure control and side effects in open-angle glaucoma between 4% pilocarpine administered