The pharmacokinetics and pharmacodynamics of azosemide were evaluated after intravenous (IV) administration of the same total dose of azosemide, 1 mgkg(-l) in different infusion times, 1 min (treatment I) and 4h (treatment II) to rabbits (n= 5, each). The loss of water and electrolytes in urine induced by azosemide was immediately replaced with infusion of equal volume of lactated Ringer's solution. Some pharmacokinetic parameters of azosemide were different between treatments I and II. For example, the mean value of terminal half-life (70.5 versus 107 min), total body clearance (5.88 versus 8.32 mL min(-1)kg(-1), renal clearance (3.45 versus 6.51mL min(-1)kg(-1), and mean residence time (18.5 versus 31.7min) increased significantly in treatment II. The 8h urine output (236 versus 733mL) and 8h urinary excretion of sodium (29.2 versus 76.4mmol) and chloride (27.5 versus 78.9 mmol) increased significantly in treatment II although the total amount of 8h urinary excretion of unchanged azosemide increased by only 15% in treatment II. This could be due to the fact that the urinary excretion rates of azosemide in treatment II remained for a longer period of time close to the maximally efficient urinary excretion rates of azosemide for both urine output and urinary excretion rates of sodium than in treatment I. Plasma concentrations of azosemide and hourly urine output and hourly urinary excretion of azosemide, sodium, potassium, and chloride during the apparent steady state (between 2 and 4 h) in treatment II were fairly constant.