Renal cortical and papillary perfusions were assessed by laser-Doppler flowmetry and autoregulatory indices. There was cortical autoregulation (autoregulatory index of 0.31 +/- 0.08) in Wistar from 160 to 100 mm Hg, but not in the papilla, which was abolished by nitrendipine, 0.125 and 0.25 micrograms kg-1 min-1. In SHRSP the cortex, but not the papilla, exhibited autoregulation from 180 to 120 mm Hg (autoregulatory index of 0.27 +/- 0.10) but not during low and high doses of nitrendipine. The non-clipped kidney cortex of 2K1C Goldblatt rats autoregulated from 190 to 130 mm Hg (autoregulatory index of 0.20 +/- 0.13), but was inhibited only by the higher dose of nitrendipine. In mature Wistar and SHRSP cortical autoregulation is blocked effectively by nitrendipine whereas the 2K1C Goldblatt hypertensive rats are relatively resistant.