A prospective study of 0.1 sec and 0.2 sec duration argon laser trabeculoplasty was undertaken in 33 patients with chronic simple glaucoma. Patients were randomly allocated to receive 0.1 sec trabeculoplasty to the eye and 0.2 sec trabeculoplasty to the other. No difference was found in the fall in intra-ocular pressure or in glaucoma control between the two durations over the six months of the study. However, 0.2 sec argon laser trabeculoplasty was reported to be more uncomfortable of 60% of patients.