The beneficial and harmful effects of 2% pilocarpine and 0.125% echothiophate iodide were evaluated on the prospective study of uniocular miotic therapy using the fellow eye as a control. Thirty primary open-angle glaucoma patients were treated with pilocarpine alone over a median time of 55 months. Twenty-nine similar patients were treated initially with echothiophate iodide and subsequently with pilocarpine over a median time of 54 months. Pilocarpine is cataractogenic but the changes are less marked and require more time than those induced by echothiophate iodide. In the combined group of 118 eves of 59 patients there were 11 optic disc changes and dix glaucomatous field defects. There was no difference in incidence between the treated and control eyes. The results suggest that one should be conservative in prescribing miotics, including pilocarpine alone, for patients suspected of having glaucoma.