This study assessed the effects of transplants of freshly isolated or cultured (ie. passaged) retinal pigment epithelial (RPE) cells from neonatal and adult normal and RCS pigmented dystrophic rats on photoreceptor cell survival in retinas of 22-26-day-old pink-eyed RCS dystrophic rats. We determined that retinas of 2-month-old RCS rats transplanted at 26 days with RPE cells of adult RCS rats did not support photoreceptor cell survival above that seen in sham or nontreated control RCS retinas, as outer nuclear layer (ONL) thicknesses were not significantly different (10.0 +/- 1.31 microns, 11.7 +/- 4.04 microns and 9.42 +/- 1.88 microns, respectively). Surprisingly, in this same transplant group, RPE transplants from neonatal RCS dystrophic rats were able to promote photoreceptor cell survival similar to that seen in transplants of neonatal Long Evans rats, as evidenced by similar ONL thicknesses (34.4 +/- 3.16 microns and 33.6 +/- 6.03 microns, respectively), but the rescue effect quickly diminished. However, in retinas of 22-26-day-old RCS rats transplanted with RPE cells from adult Long Evans rats, the level of photoreceptor cell rescue was approximately 48% (ONL: 19.6 +/- 2.79 microns), when compared to retinas transplanted with RPE cells from neonatal Long Evans rats, but significantly greater than that caused by transplants of RPE cells from adult RCS rats.(ABSTRACT TRUNCATED AT 250 WORDS)