A preliminary study of ten patients with glaucoma, each of whom has undergone laser trabeculoplasty to one or both eyes, is presented. Tonography-on-treatment was performed on each patient approximately four weeks prior to laser, and repeated approximately ten weeks afterwards. Central fields and anterior chamber depth measurements before and after laser trabeculoplasty are also presented. Intraocular pressures fell by a mean of 12.34 mm (SD +/- 8.5, range 3-23) in all 12 lasered eyes. Central fields improved in ten eyes, and the anterior chamber of treated eyes became shallower by an average of 0.27 mm, compared with untreated eyes (p less than 0.05). Po/C values improved in 11 treated eyes. Very little attempt was made to alter medical treatment during the period outlined above.