The glucose metabolism effects of six hour exposures to subarachnoid injections of metrizamide, iohexol, iodixanol and control solutions were studied in vivo in 18 rabbits. The brain tissue uptake of intravenously injected 14C labelled deoxyglucose was measured using auto radiographic techniques. Metrizamide and iodixanol caused significant (p < 0.05) decreases in deoxyglucose uptake in the outer cortical areas where the contrast medium concentrations were highest. Iohexol and the control CSF solution did not cause significant effects. The results appear to indicate that iohexol has less effect on brain tissue glucose metabolism than either metrizamide or the new non-ionic dimer iodixanol.