A retrospective survey was performed on 22 patients with chronic simple glaucoma who had undergone a single repetition of argon laser trabeculoplasty. Two groups were identified who had received treatment with either 0.1 or 0.2 sec duration. The 0.2 sec group showed a reduction in the medications used, in addition to a comparable fall in intra-ocular pressure to the 0.1 sec group, and had a lower rate of drainage surgery. These findings may have arisen because of the higher energy delivered as a result of the longer duration employed. However, there are risks of repeating argon laser trabeculoplasty: one patient in the 0.2 sec group developed a rise in intra-ocular pressure of 15 mmHg following the repeat treatment, and required drainage surgery one month later.