The clinical significance of the urinary oxygen tension (PuO2) was evaluated in 60 patients with ischemic heart disease. The PuO2had fair relations to cardiac index and serum creatinine level (r = 0.73 and r = 0.73, respectively). Although the PuO2had a fair relation to serum creatinine in patients with a low cardiac index, there was no relation to the cardiac index. In patients with increases in PuO2from day 1 to day 2, the cardiac index increased, and the serum creatinine level decreased on the 2nd day, whereas a sustained decrease in cardiac index and an increase in serum creatinine were observed in patients with a decrease in PuO2from day 1 to day 2. Thus, PuO2 can be used as an indicator of the renal function in patients with ischemic heart disease.