The determination of potency as well as of the peak and duration of action of drugs in man poses many problems, especially when dealing with agents which have prominent effects on the central nervous system. Frequently assay is attempted in patients who are suffering from ill-defined abnormalities and who are often under known or unknown drug treatments. Furthermore the determination of drug effects is usually based upon direct or indirect subjective appraisals. In 1936, Seevers and Pfeiffer1 investigated the effect of analgesic agents. Instead of using patients they used normal volunteers. From the data thus collected they were able to draw curves for the effect of analgesics which are still the most accurate available for the agents studied. Similar rationale suggests that valuable knowledge could be gained about the effect of anti-anxiety drugs by objective measurements in normal volunteers. The quantitative electroencephalographic method of