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As previously reported in the literature, hyperbaric oxygen delivery seems to modify the natural course of retinitis pigmentosa. In order to evaluate these first encouraging data, 48 affected subjects were separately studied in two subgroups (cases and controls). All patients underwent yearly an ophthalmological examination completed by a maximum amplitude electroretinogram, conducted according to our 'differential derivation' system, a new recording technique specifically designed to enhance the signal-to-noise ratio. Oxygen delivery was provided regularly for 90 min daily (2.2 Absolute Atmosphere) in three cycles according to a standard protocol. In the cases, electroretinographic mean values were as follows: at T0 (basal) 4.68 +/- 3.81 microV; after one year (T1) 8.46 +/- 5.71 microV; at two years (T2) 10.7 +/- 7.6 microV; at the end of the study (T3) 14.4 +/- 11.7 microV. In the controls, electroretinographic mean values were as follows: at T0 4.92 +/- 3.05 microV; at T1 5.04 +/- 3.07 microV; at T2 3.46 +/- 2.77 microV: at T3 2.97 +/- 3.61 microV. Amplitudes showed a remarkable (p<0.001) increase in the cases, while a slightly significant (p<0.02) decrease was evident at the end of the study in the controls. In our opinion, retinal oxygen availability may be critical in retinal degeneration and hyperbaric oxygen delivery, inducing hyperoxia, seems to be able to bring about the rescue of the retinal photoreceptors helping them in their metabolic requirements. Unfortunately, our study demonstrates an increase in electroretinographic responses only, which may not necessarily also mean an evident change in visual acuity.