A HPLC method has been developed to determine the concentrations of SAZ-VII-23 (3-benzoyl-7-isopropyl-3,7-diazabicyclo[3.3.1]nonane HClO4), a novel antiarrhythmic agent, in dog plasma and urine. Plasma treated with acetonitrile and alkalinized urine were extracted with chloroform- propanol (9:1). An aliquot was injected on to HPLC system using a C6reversed-phase column and acetonitrile-methanol-37.5 mM phosphate buffer, pH 6.8 (28.5:28.5:43 v/v) containing 4.0 mM triethylamine as mobile phase. Detection wavelength was 255 nm. The linear range were 0.04–8 μg/ml, and the lower limit of quantitation was 0.04 μg/ml in plasma and urine, respectively. The method was applied to determine plasma and urine concentrations and preliminary pharmacokinetic profiles of SAZ-VII-23 in a dog.