An error appeared in the abstract of the article “The Relationship of Regional Cerebrovascular CO2Reactivity to Blood Pressure and Regional Resting Flow” by Robert H. Ackerman, M.D., which appeared in STROKE, volume 4, page 725 (September-October) 1973. The following is the corrected abstract.Cerebrovascular CO2reactivity (the change in cerebral blood flow per mm Hg change in PaCO2) is shown to be directly related to resting flow and inversely related to blood pressure for regional as well as for mean CBF data. Both regional and mean CO2reactivity therefore are proportional to the ratio resting flow/blood pressure. This ratio is the reciprocal of resistance and may be calledconductance. When regional CO2reactivity for 428 cerebral areas is plotted against an approximation of regional conductance, the data describe positive linear relationships similar to those found when mean CO2reactivity is plotted against mean conductance. These relationships can be demonstrated whether CO2reactivity is calculated with specific or percent change in flow. The data suggest that under physiological conditions CO2reactivity is related to the basal tone of the cerebrovascular bed. The way in which CO2reactivity relates to conductance, therefore, may be a more reliable index of the integrity of the cerebrovascular CO2response than the CBF change per se. Analysis of CO2reactivity as a function of conductance may facilitate the interpretation of mean and regional CO2reactivity and may provide a more meaningful basis for comparison of the CO2response between individuals.