We have looked for inflammatory lesions in 37 patients using granulocytes labelled in vivo. For the purpose of cell labelling we used a monoclonal murine antibody reacting with NCA and carcinoembryonic antigen (CEA) (BW 250/183) labelled with 99Tcm. All abscesses and other inflammatory lesions were visualized with excellent quality scintigrams between 2 and 6 h after the injection. As the antibody can be stored in a freeze-dried form and labelled at any time in any department of nuclear medicine with 99Tcm without cell separation being necessary, the method appears to be suitable even for use in acute diagnosis. No side effects have so far been found.