To the Editor.— Hansen and co-workers1 have taken the time to address a question of considerable import, ie, whether the use of Doppler continuous wave forms provides a means of reflecting changes in brain blood flow when the anterior cerebral artery is used. The question is important because of the conclusions that may result from the use of this technique in clinical research.2 Although Hansen et al report a high correlation and significant P value for the relationship between measurements of blood brain flow and the area under the velocity curve, peak systolic velocity, and end diastolic velocity, these are representative of nonlinear relationships as noted by the authors.