Rat lens γ-crystallins were separated by preparative flat bed isoelectric focusing (pH 7–11). The fractions obtained were submitted to analytical isoelectric focusing, fused rocket immunoelectrophoresis and immunodiffusion. The results demonstrate that rat lens γ-crystallins are electrophoretically and immunologically heterogenous. Evidence is given that there are two immunologically different groups. Rat γ1-crystallin, the prominent and immunologically homogeneous part, is identical to calf lens γ-crystallin. The second group of proteins, γ2-crystallins, is heterogeneous and shows only partial identity with γ1 crystallin.