alpha B crystallin is a lens protein which has homology with the small heat-shock proteins and is also expressed in non-lenticular tissues. Polyclonal antibodies have been raised to a synthetic peptide corresponding to residues 1-10 of alpha B crystallin. The antiserum detects a 20 kDa polypeptide on nitrocellulose replicas after polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate of extracts of heart muscle known to be rich in alpha B crystallin. Staining of normal human tissues reveals immunoreactivity of lens capsular epithelium, skeletal muscle, cardiac muscle, smooth muscle, renal tubular epithelium, Schwann cells, and glial cells, as has been described by other workers. In addition, positive staining of normal thyroid epithelium, colonic epithelium, and stratified squamous epithelium was seen. Tissues known to contain ubiquitinated inclusion bodies were immunostained with the anti-alpha B-crystallin antiserum. Staining of cortical Lewy bodies, astrocytic Rosenthal fibres, and hepatic Mallory bodies was seen, but only a proportion of inclusions were positive. Neurones containing the ubiquitinated inclusions of Alzheimer's disease were only very rarely immunostained and the ubiquitinated inclusions of motor neurone disease were not detected by the antiserum. Reactive astrocytes in cerebral tissues were strongly immunostained. The results suggest that alpha B crystallin is involved in the formation of ubiquitinated inclusion bodies that have associated intermediate filaments and support previous observations on the localization of a brain-specific ubiquitin carboxy-terminal hydrolase which similarly divides ubiquitinated filamentous inclusions in the central nervous system into two main groups.