SummaryAn electrophotometric method is described which gives records of the volumetric variation of the pulse with great accuracy. The method has been used to study the vasodilatator effect of some drugs.Intravenous administration of nicotinic acid or of 2 benzyl 4-5 imidazoline chloride definitely increases the volumetric variation of the pulse. This increase is of short duration, but is noticeable in several parts of the body.