A method has been devised by which neutral glycerides may be determined in 0.1 ml. of whole blood. Lipid is extracted from the blood with alcohol–ether, dissolved in chloroform, and saponified. The liberated glycerol is then oxidized with periodic acid and the resulting formaldehyde distilled into sodium sulphite solution. The distillate is then reacted with chromotropic acid and the resulting color measured with a photoelectric colorimeter. A correction for formaldehyde derived from phospholipid may be applied if the blood lipid phosphorus level is known. The results of some typical analyses of blood from normal and diabetic subjects are given.