The general pharmacological properties of a combination of the angiotensin converting enzyme (ACE) inhibitor moexipril hydrochloride (CAS 82586-52-5) and the thiazide diuretic hydrochlorothiazide (CAS 58-93-5, HCTZ), ratio 7.5 + 12.5, were studied in generally accepted models in vitro and in vivo. In vitro, the combination showed neither agonistic nor antagonistic activities on the isolated guinea pig trachea in concentrations up to 2 x 10(-4) g/ml. In mice, there was no effect on intestinal motility or the thiopental-induced sleeping time up to 1000 mg/kg. The only activity observed in mice was an inhibition of spontaneous motility after oral dosing with 300 and 1000 mg/kg, respectively. Both HCTZ (1-10 mg/kg) alone and the combination moexipril/HCTZ (1.6 or 4.8 mg/kg) produced dose-related increases in diuresis and electrolyte excretion in rats, however, without any potentiating effects for the drug combination. On the cardiovascular system of anaesthetised dogs, the effects observed were as expected, e.g. dose-related decrease in blood pressure. Repeated dose toxicity studies in rats and dogs revealed the kidney as target organ. This effect, based on highly exaggerated pharmacological activity, is well-known for other ACE inhibitors. No potential for teratogenic effects could be observed for the drug combination. In summary, the preclinical data indicate that the combination of moexipril and HCTZ (ratio 7.5 + 12.5) represents a safe drug without relevant side effects or gross toxicity.