Abstract: Dihydroetorphine reacts with tropaeolin OO Ⅳ to form a complex which can be extracted with chloroform. After reducing with zinc in HCl solution, tropaeolin OO Ⅳ phosphoresces strongly with a sensitivity of 2 ng, and the intensity is proportional to the amount of dihydroetorphine present. The method may be used for the determination of dihydroetorphine in biological materials.One and five minutes after im administration of dihydroetorphine 0.1, 0.2, or 1 mg/kg to rabbits, the blood and brain drug concentrations were determined. Linear relationships between dosage used and blood, and brain drug concentrations were obtained as the following equations:Blood: Y=100.6X+17.73 (for 1 minute)Y=367.8 X+4.34 (for 5 minutes)Brain: Y=5363 X+275.4 (for 1 minute)Y=6084 X+1022 (for 5 minutes)where Y=drug concentration (ng/ml or g), X=dosage of dihydroetorphine used (mg/kg).