180 eyes of 97 patients with primary open angle glaucoma and IOP greater than 22 mm were treated for more than 3 years with timolol-maleate. 130 eyes had glaucoma simplex, and 50 eyes had glaucoma capsulare. With timolol maleate as the only medication after 3 years, the IOP was controlled in 33% of the glaucoma simplex group, and in 8% of the glaucoma capsulare group. No serious local or systemic side-effects were observed.