The effects of dopamine (10 micrograms/kg/min i.v.) upon intrarenal microcirculation, total, superficial cortical and outer medullary blood flows and outer medullary pO2 were continuously determined in anesthetized rats with ultrasonic and laser-Doppler probes and oxygen microelectrodes. While total and cortical flows were unaffected, outer medullary flow increased by 35 +/- 5% (mean +/- SE, p < 0.01). Outer medullary pO2 was not significantly altered (from 16 +/- 4 to 18 +/- 4 mm Hg). In volume-expanded rats total and cortical flows rose as well. In rats pretreated with indomethacin, with or without N omega-nitro-L-arginine methyl ester HCl, dopamine restored renal microcirculation and ameliorated outer medullary hypoxia.