We determined the lactate concentration in 112 samples of arterial blood, simultaneously by two-different technic: 1) The usual enzymatic technic (plasmatic and intracellular lactates). 2) A new technic using an enzymatic lactate sensor ("lactate analyzer 5400") which measures the plasmatic lactates only. The data obtained with the two technics were very similar (r = 0,982). The small volume of blood used and the handiness and rapidity of the new procedure are to be noted.