Microglial activity, as measured by PBR28 distribution volume ratio, is elevated in subjects at ultra high risk of psychosis (df=21 p=0.004) and patients with schizophrenia (df=21 p<0.001) in the total grey matter, frontal and temporal cortical regions of interest but not in control regions (the cerebellum and brainstem). The mean regional distribution volume ratios are shown for each group together with those for matched controls. The results of the ANCOVA covarying for age and translocator-protein genotype are shown for each case-matched control comparison