Four children with cyanotic congenital heart disease, who were studied for the complication of brain abscess, are described.An earlier stage of "cerebritis" is compared to the later stage of localized suppuration in relation to the finding of 2 types of radiographic procedures: the isotope brain scan as a test of function and air encephalography or arteriography as a test of structural alteration.The importance of these studies in planning the clinical management of these patients is discussed. It is noted that an initially positive brain scan may occur at a time when the lesion is not yet suitable to surgical drainage. It appears that such drainage had best be delayed until the test of structure, the contrast roentgenographic procedures, also indicate a localized mass lesion.