The hypotensive effects of anaritide (Wy-47,663), a 26 amino acid atrial natriuretic factor, were examined in conscious, monocrotaline-induced chronic pulmonary hypertensive rats. Anaritide (0.25-8 micrograms/kg per min i.v.) decreased systemic arterial pressure at 2-8 micrograms/kg per min by as much as -15.6 +/- 0.4 mm Hg. The pulmonary hypotensive response to anaritide was not different from vehicle treatment. We conclude that anaritide is more effective in decreasing systemic than pulmonary arterial pressures in monocrotaline-induced pulmonary hypertensive rats.