The efficacy of argon and diode laser photocoagulation of the avascular peripheral retina for threshold retinopathy of prematurity (ROP) was compared in a prospective trial. The study group included 9 premature infants (17 eyes). In each infant, one eye was treated with the diode laser indirect ophthalmoscope (LIO), and the fellow eye was treated with the argon LIO. Supplemental oxygen therapy was administered after laser treatment to all nine infants. The mean duration of the follow-up period was 9.7 +/- 2.6 months. All 17 eyes (100%) had complete regression of ROP and favorable outcomes. The diode and argon LIO appear to be equally effective in treating threshold ROP. Two patients sustained burns of the tunica vasculosa lentis and anterior lens capsule in the argon laser treated eye but not in the fellow diode treated eye. Photocoagulation with either the diode or argon LIO, combined with supplemental oxygen treatment, appears to be a promising treatment for retinopathy of prematurity.