The effect on macular function of the wavelength of laser light used to treat proliferative diabetic retinopathy was studied. Thirty-six eyes of 25 patients received panretinal photo-coagulation according to a standardised protocol and before and at intervals after the treatment were tested by a battery of macular function tests. Each eye was randomly assigned to treatment with blue-green, yellow, or orange laser. The tests included best corrected visual acuity, colour vision, contrast sensitivity, macular threshold, and central visual fields. There were no significant differences in the results of these tests between the three treatment groups, though there was wide scattering of baseline values within each group. Laser wavelength has not been shown to be an important determinant of central visual function following panretinal photo-coagulation in patients with proliferative diabetic retinopathy within the wavelengths tested.