A selective and simple HPLC procedure has been developed to determine histidine (His) and histidinol (HDL) in liver supernate. The separation was performed on a column, Mightysil RP-18 GP. The eluted analytes were measured with UV detection without derivatization which provided detection limits of 1.1 and 2.0 microM for His and HDL (S/N ratio, 3:1), respectively. Recovery of the analytes added to liver sample was 98.3-101.6% within a 1-day study and 95.7-98.6% on different day (6 days) studies. The apparent histidinol dehydrogenase activities (nmol/g wet tissue) at pH 8, 9, 10, 11, and 12 were 38.6, 50.4, 160.3, 274.3, and 185.6 for liver; 90.6, 132.2, 30.7, 22.1, and 6.76 for kidney; 0.0, 0.0, 38.2, 20.1, and 12.9 for pancreas; 0.0, 0.0, 0.0, 14.7, and 6.8 for spleen; 0.0, 0.0, 4.2, 6.8, and 0.0 for muscle; and 0.0, 0.0, 4.9, 1.8, and 0.0 for small intestine, respectively. On the basis of optimum pH values, histidinol dehydrogenase activity in the organs was in the following order: liver>kidney>pancreas>spleen>muscle>small intestine.