Plasma levels of lidocaine were determined in either 10 patients following injection into the deltoid and lateral vastus muscle, respectively. We used an automatic injector containing 250 mg of lidocaine in a 10% solution. In the early phase after injection, plasma levels were higher, when the deltoid muscle had been chosen for administration. This was the same result as referred by other authors using normal injectors. Variance of single plasma values was smaller in the vastus group.