The pharmacokinetics and pharmacodynamics of EXP3174 (2-n-butyl-4-chloro-1-[(2'-(1H-tetrazole-5-yl)biphenyl-4- yl-)methyl]imidazole-5-carboxylic acid), an angiotensin II receptor antagonist, were studied in conscious rats. Elimination half-life, systemic clearance, and apparent volume of distribution of EXP3174 at a dose of 10 mg/kg i.v. were 2.9 h, 1.8 ml/min/kg, and 0.25 l/kg, respectively. Inhibition of the angiotensin II pressor response correlated with the log of the steady state plasma EXP3174 concentration in a sigmoidal fashion with an IC50 of about 200 ng/ml. When corrected for plasma protein binding, the IC50 (free) for EXP3174 was 0.4 ng/ml (0.9 nmol/l). This study indicates a predictable plasma concentration-effect relationship of EXP3174 in rats which would be helpful in designing more rational dosing schemes for pharmacodynamic studies.