We studied renal function using a positron emission tomography with C15O gas and 68Ga-EDTA in 6 normal subjects (male, 21-77 years old). The blood volume (ml/100 g (kidney] was 19.2 +/- 1.8 for the one 21 years old subject and 11.8 +/- 2.0 for the rest (65-77 years old). The glomerular filtration rate (ml/min/100 g (kidney] was 57.8 +/- 1.1 for the 21 years old subject and 30.4 +/- 2.8 for the rest.