alpha-Crystallin, a tissue specific structural protein of the ocular lens, is known to be composed of two subunits, alpha A and alpha B. By using a specific antibody in an immunoblotting procedure we have found that one of the subunits, alpha B is present in a number of non-lenticular tissues including the retina, heart, skeletal muscle, skin, brain, spinal cord and lungs. Interestingly, in the rat, this protein is present in significantly higher concentrations in adult than in fetal tissues and, with the exception of the lens, fetal and adult heart has the highest concentration among the tissues examined. That the protein in question is, in fact, alpha B, was confirmed a) by the remarkable similarity of Staphylococcus aureus protease peptide maps of the protein in the heart and purified alpha-crystallin and b) by the sequence analysis of a rat heart cDNA clone identified by the alpha B antibody. Based on these observations we conclude that while alpha A has a tissue-specific role, alpha B is a polypeptide of independent function not restricted to the ocular lens.