The effects of 1 day of single nephron, unilateral ureteral (UUO), and bilateral ureteral (BUO) obstruction on tubuloglomerular feedback were studied in anesthetized rats. Stop-flow pressure (SFP) was measured as an index of glomerular capillary pressure before, during, and after loop of Henle microperfusion. Tubuloglomerular feedback (delta SFP) showed an increased sensitivity to low loop perfusion rates and an increased maximal response after 1 day of single nephron obstruction or relief of UUO. Tubuloglomerular feedback was not significantly different from normal after release of BUO. Whole kidney glomerular filtration rate (GFR) was about 10% of normal after release of ureteral obstruction, and single nephron glomerular filtration rate (SNGFR) averaged one-third of normal. Paired measurements of SNGFR from proximal and distal tubules revealed no significant differences in control or in BUO kidneys, but a significant proximal-distal SNGFR difference was observed after UUO. The results suggest that tubuloglomerular feedback does not significantly contribute to the low GFR after release of BUO; after release of UUO, approximately one-fourth of the fall in GFR may be due to activation of the feedback mechanism.