The thymidine analogue bromodeoxyuridine (BrdU) has a long, colorful history of heavy use in molecular and cytokinetic studies (1, 2). BrDU is incorporated into newly synthesized DNA only in S-phase cells, and then immunocytochemically detected with BrDU antibodies. This method allows for extremely accurate and comprehensive comparative studies of a variety of cells ranging from normal to neoplastic.