β-actin is one of the six different actin isoforms that have been identified. The actin molecules found in cells of various species and tissues tend to be very similar in their immunological and physical properties. As a consequence, it has been difficult to produce potent antisera against this protein. Therefore, the availability of monoclonal antibodies to ß-actin provides a useful and specific tool in the study of the intracellular distribution of β-actin and the static and dynamic aspects of the cytoskeleton.