Computerized threshold perimetry of the central 30 degrees was performed on 69 eyes of 36 patients (men and women of all age groups and with different types of diabetes) one day before and one month after panretinal photocoagulation by argon laser. An average of 900 spots were placed in a chessboard pattern in three sessions (central size 100 microns, midperiphery 200 microns, periphery 500 microns). Only patients with a visual acuity of 20/60 or better were admitted to the study. Twenty-seven (39%) of the eyes examined had absolute scotoma (corresponding to spot III/4 on the Goldmann perimeter) even before photocoagulation; in 20 eyes (29%) some new absolute scotomata, albeit small, were seen. In the outer ten degrees of the central visual field area examined relative scotomata are the average finding. The macular region showed no threshold reductions.