Development of a technique for measuring the oxidation rate of a 14C-labelled substrate from 14CO2 production without the need for collection of expired air.

1. A method is proposed for the determination of the rate of oxidation of 14C-labelled substrates in man from blood sampling only. 2. The method was verified by simulating release of 14C into the bicarbonate pool of patients by using a constant-rate infusion of sodium [14C]bicarbonate, the plasma level of total 14CO2 (d.p.m. ml-1 70 kg-1) correlating well (r = 0.878, P = 0.001) with the infusion rate (microCi/h). 3. Techniques involved in employing this method are discussed, particularly in the light of errors involved.