Summary: Local cerebral blood flow was measured in five regions of rat cortex immediately following intrave nous administration of the ,),-aminobutyric acid (GABA) agonist muscimol. In contrast to recent observations, no increases in blood flow were found at either of the two time points analysed, and the data revealed that de creases in blood flow previously reported 30 min after muscimol treatment were in evidence as early as 30 s. These results are totally consistent with the conclusion