The specialized research center with more than 4000 patients on file with retinitis pigmentosa proposes a clinical trial to determine whether a nutritional supplement will slow the course of the common forms of retinitis pigmentosa. Two hundred and twenty patients who meet a preset list of eligibility criteria will be randomly assigned to either a treatment or a control group and followed annually over a period of 5 years. Static perimetric thresholds measured with the Humphrey Field Analyzer will be used as the primary outcome measure. Electroretinogram amplitudes and visual acuities will be monitored as secondary outcome measures. The trial will be conducted with a double-masked protocol. Collaborative arrangements have been made for biochemical analysis of blood specimens to monitor safety and compliance. Results will be followed by an outside Data Safety and Monitoring Committee.