In the many emergency situations in which it is difficult or impossible to obtain venous access rapidly endotracheal drug therapy can be effective and life saving. Yet relatively little is known about endotracheal drug therapy. Plasma lidocaine levels were measured in 23 dogs after the administration of endotracheal lidocaine at a dose of 2 or 4 mg/kg. Endotracheal lidocaine was given either as a dilution with normal saline (1:1 dilution) or undiluted (Group 1, no dilution; Group 2, dilution). Significantly higher plasma lidocaine levels occurred with the dilution group in all the time periods and with either dose of lidocaine (2 or 4 mg/kg) (P less than .001). Mean plasma lidocaine levels (microgram/mL) at five minutes were: (at 2 mg/kg dose) Group 1, 0.64; Group 2, 3.4; and (at 4 mg/kg dose) Group 1, 1.9, Group 2, 4.7 (P less than .001). Arterial blood gases were not significantly different before or after endotracheal drug administration. This study suggests that higher plasma lidocaine levels are achieved and maintained longer when diluted with normal saline than when given undiluted; and higher plasma lidocaine levels can be obtained by dilution without any detrimental effect on respiratory function as measured by arterial blood gases.