OBJECTIVE To study the effect of electric and chemical stimulation of locus coeruleus (LC) on arterial pressure and renal sympathetic nerve discharge activity (RSA). METHODS Electric stimulation of LC and microinjection of L-glutamate (L-Glu), morphine, and GABA into the LC of rabbits were made. The LC was destructed electrolytically. Arterial pressure and RSA were recorded. RESULTS Both electric stimulation (150 microA, 50 Hz) of the LC and microinjection of L-Glu (0.5 mumol) into unilateral LC elicited increases in arterial pressure (13.5 +/- 0.3 vs 19.5 +/- 0.8 kPa, P < 0.01 and 13.8 +/- 0.4 vs 17.5 +/- 0.8 kPa, P < 0.01, respectively) and RSA (by 107 +/- 14%, P < 0.01, and 88 +/- 21%, P < 0.01, respectively). Microinjection of morphine or GABA did not induce any significant changes in the above two parameters. Electrolytic lesion of the LC eliminated the pressor response induced by microinjection of L-Glu. CONCLUSIONS Excitation of LC has a pressor effect in rabbits, but LC is not a crucial nucleus in tonic regulation of blood pressure.