The effect of various drugs on hemispheric and regional cerebral blood flow (CBF) was investigated in a total of 410 patients. While a few drugs (midodrin, proxazole, vincamine, hexobendine, extract of ginkgo biloba, dextran and ouabain) were able to improve hemispheric CBF, only ephedrine combined with xanthines decreased CBF. For vincamine the dependency of the effect on certain plasma levels was established. Only ouabain of the tested cardiac glycosides effected CBF; their similar hemodynamic actions suggest here an influence of ouabain on cerebral vessels. For the evaluation of drug effects on rCBF the detection of heterogeneous responses is important. Such responses may be quantified by regression analysis. While intracerebral steal effects were observed only under certain circumstances, inverse cerebral steal phenomena may be caused by diverging actions of several drugs. If treatment is aimed at improvement of cerebral hemodynamics, only drugs with a demonstrated effect, at least on perfusion of ischemic regions, should be employed.