To the Editor.— In a recent issue of this journal (Pediatrics. 1993;91:414-417), Dr Deborah Hirtz reported on a Workshop on Near Infrared Spectroscopy (NIRS), organized by the National Institute of Neurological Disorders and Stroke (NINDS). NIRS is becoming increasingly accepted as a method for noninvasive monitoring of cerebral hemodynamics and oxygenation in the newborn and recently in the fetus during labor. However, as Dr Hirtz carefully pointed out there are still many technical problems to be solved, and considerable controversy about the quantitation and interpretation of MRS data especially the redox state of cytochrome oxidase.