Lactate concentration was determined in 112 samples of arterial blood, simultaneously by 2-different techniques; the usual enzymatic technique (plasmatic and intracellular lactates) and a new technique: using an enzymatic lactate sensor (lactate analyzer 5400) which measured plasma lactates only. The data obtained with the 2 techniques were similar (r = 0.982). The small volume of blood used and the handiness and rapidity of the new procedure are important.