Abstract
The fluorescent antibody technique has been applied for the demonstration of mouse isoantigens at the cellular level. Specific reactions were obtained by the indirect or "sandwich" technique with a variety of living normal and neoplastic cells. Isoantigens of the H-2 system and of other systems could be demonstrated as well and appeared to be localized at the cell membrane. As far as the H-2 system was concerned, the membrane localization could be confirmed on histological sections.