Methods of using intramuscular lignocaine and its relay with an intravenous infusion were studied in 34 patients with reference to serum levels. A first group of 9 patients with myocardial infarction received an intramuscular injection of 300 mg lignocaine into the deltoid or gluteral muscles at five day intervals. The deltoid appears to be the better site of injection in patients confined to bed because of its quick absorption, higher serum levels between the 15th and 90th minute (+47%), and longer duration of action (180 compared to 120 minutes). The difference is not observed in ambulatory patients and seems to be related to sluggish circulation in the gluteral muscles during bed rest. Its relay with intravenous infusion was studied in 14 patients. In the first 6 patients, intradeltoid injection was immediately followed by an infusion of 2.5 mg/mn, giving an average plasma lignocaine level between the 15th and 60th minute greater than 5 mu/ml. In the 8 other patients, a period of I hour was allowed to elapse before starting the infusion. The plasma levels were found to be within the therapeutic range in all patients and no side effects were observed. The administration of an intravenous infusion of 150 mg/hr of lignocaine for 48 hours led to excessively high plasma levels in 8 patients at the 24th hour, 3 of whom had side effects. Reducing the dosage to 100 mg/hr from the 12th hour onwards in II patients avoided this complication. A 300 mg intradeltoid injection of lignocaine is easy to give in the patient's home and therefore, is the best adapted method for the pre hospital treatment of myocardial infarction. When necessary, it may be relayed with an intravenous infusion one hour later, in the coronary care unit.