The purpose of this study is to investigate salient diagnostic features of the brain abscess in RI brain scanning. In 27 patients with brain abscess, 37 scannings were performed in the various stages of their clinical courses. The results were positive in all cases. Among 27 cases, ten cases were investigated by means of the ISOCOUNT SCANNING SYSTEM, the technical detail of which was reported previously. It was proved that the isocount scanning method combined with the multilevel analysis was more sensitive diagnostic aid than the conventional RI scintigraphy. Using the newly developed method, it was not difficult to diagnose the brain abscess in its early stage, even in the stage of presuppurative cerebritis. Doughnut sign was seemed to be more frequently visualized by this method. Surgical indication of the brain abscess was discussed from nucleomedical view point, and it was emphasized that so-called doughnut sign in brain scanning would indicate the appropriate stage of the brain abscess to be operated on.