Changes in the distribution of γ-crystallins in the lenses of rats between 1 and 52 weeks of age were studied by isoelectric focusing. Generally levels of components with high isoelectric pointwere depressed while those with low isoelectric point were elevated during this time. The in vitro incorporation of <sup>14</sup>C amino acids by those components decreasing in level was diminished with increasing age, while an enhancement of incorporation was found for components increasing in level. Evidence that the components present at high levels in the nucleus (i.e.: the oldest part of the lens) are converted to urea-insoluble material is given.