The application of infrared absorption spectrophotometry to the mass screening of human serum for elevated triglyceride levels has been investigated, and results in both normal and elevated ranges have been compared with values obtained by manual and automated procedures. By means of a simple technique serum samples were scanned with a typical instrument, and the difference in absorbance at 1,740 and 1,725 cm-1 was plotted vs. triglyceride concentration to prepare a Beer-Lambert plot; several hundren serum samples were then determined with the plot, and results were compared with those from two independent methods with good agreement. Significantly elevated serum cholesterol ester levels gave high values, but this was not considered a disadvantage in view of the general screening nature of the determination. The standard deviation at 160 mg/dl was found to be 13. The infrared method is presented at a viable mass screening procedure; it is not proposed that it supplant presently available laboratory procedures for routine use at this time. Advantages of the infrared method include simplicity, rapidity, low supply cost per test, and small sample volume.