Purpose. Basic fibroblast growth factor (bFGF) has been shown to enhance survival times of isolated human rods and to rescue photoreceptors in vivo in rat retina. We have followed the degeneration of the outer segments of rat and human rods in acute cultures, in the absence and presence of the growth factors bFGF, BDNF and GDNF. This isolation approach can identify which survival-enhancing compounds act directly on photoreceptors. It may also be useful for observing changes in responsiveness or sensitivity to growth factors due to aging or disease state; for example the upregulation of bFGF in developing rd mouse (Gao & Hollyfield 1995; Dev. Biol. 169:168-84.) Methods. Single rods were mechanically dissociated from freshly-isolated rat or human retinas and put in short term culture (< 24 hr.). The cells were superfused with simple media containing BSA and either bFGF (25 ng/ml), BDNF (25ng/ml) or GDNF (0.1μg/ml). Overtime, decreases in length of aboul 12 outer segments per experiment were observed. The times required to reach 50% (T50) of the starting outer segment length were averaged for untreated and treated cells from the same retina and compared statistically using the Student t test. Results. The most striking result was the absence of any significant effect of bFGF in promoting survival of rat outer segments in young animals or adults. Tissues from younger animals (5 wks.) survived longer and showed more prominent BDNF and GDNF effects than tissues from adults (2-3 mos.). GDNF had little effect on adult rat and human rods except at higher dosages (1μg/ml) in young rat tissues. BDNF gave the most consistent results promoting increased outer segment survival times. Conclusions. It now appears that the protective effect of bFGF injections into the eyes of ischemic, light damaged or dystrophic RCS rats is due to an upregulation or unmasking of FGF receptors on rod photoreceptors themselves as these are not present or not responsive on cells from normal animals between 5 and 13 weeks old. BDNF may be a developmental or constitutively active factor, but younger, aged and light damaged animals must first be evaluated.