The bovine lens multicatalytic proteinase complex (MFC) (MW 700 kDa) comprises at least twelve subunits in the molecular mass range 22–35 JcDa. Three of the subunits, LI (27 kDa), L2 (24 kDa) and L3 (29 kDa), were purified by reverse phase HPLC. Their amino acid composition and N-terminal sequences indicate that they are not identical. LI and L2 subunits show very high (>90%) sequence homology with specific subunits of rat liver and human reticulocyte MPC and these are considered to be homologous components of the MPC which are highly conserved in evolution.