Seven patients with gyrate atrophy and deficiency of ornithine-delta-aminotransferase were studied for in vivo pyridoxine responsiveness; three responded to oral vitamin B6 with over 50% reduction of serum ornithine levels and return to normal of serum lysine levels. Electrophysiologic studies were performed on two B6-responsive patients and one B6-nonresponder over various time periods with and without pyridoxine supplementation. Electroretinogram (ERG) amplitudes improved 100% in one patient when initially given high doses of vitamin B6. Electro-oculogram light-to-dark ratio also improved for this patient. Withdrawal followed by resumption of B6 supplementation was associated with mild worsening followed by improvement of ERG responses respectively in both patients. Long-term follow-up will be needed to assess whether pyridoxine treatment will slow or halt the progression of the disease.