Fibroblast growth factor (FGF) is a potent inducer of fibre differentiation in lens epithelial explants from neonatal rats. Previously, using explants prepared from the central region of the lens epithelium, we showed an age-related loss of ability to accumulate fibre-specific crystallins in response to basic FGF. These studies have now been extended to include the peripheral region of the lens epithelium. Firstly we cultured explants from the central or peripheral regions of neonatal lenses with varying doses of FGF for 5 days, then determined how much fibre-specific beta-crystallin they had accumulated. The concentration of FGF required to induce a half-maximal response was lower for peripheral than for central cells (7 ng ml-1 compared with 36 ng ml-1). We then compared the ability of peripheral explants from 3-, 21-, 100- and 175-day-old rats to undergo fibre differentiation during culture with FGF for 13 days. In these studies alpha-, beta- and gamma-crystallins were localized in explants or quantified by ELISAs. There was an age-related decrease in responsiveness to FGF, as already observed for central explants; however, unlike central explants, peripheral explants from the oldest rats still retained the ability to respond to FGF by accumulating beta-crystallin. This suggests that FGF in the eye may play an important role in inducing lens epithelial cells at the lens equator to differentiate into fibres throughout life.