samples of a constant concentration of urea nitrogen, and the fluorescence was measured. As seen in Figure 1, the fluorescence increased as the amount of sulfuric acid increased. The maximum fluorescence intensity occurred after the addition of 0.3 ml. Further addition caused a decrease in the intensity of fluorescence. This was the amount of acid selected for use in the procedure.The specificity of this reaction for urea has been discussed in previous publications (2,10,12). These authors show that contribution by similar compounds such as uric acid, etc., is relatively insignificant due to their minute presence in these samples.A preliminary effort to adapt this procedure to the Coleman Model 12C photofluorometer has thus far proved unsuccessful. This may be the result of poor resolution of the filter system which we have employed. Work is continuing on this modification in instrumentation.