Electrically induced release of 3H-noradrenaline from superfused rat brain cortex slices was completely inhibited by tetrodotoxin (1 microgram/ml) if 0.5 or 1 V stimuli were used, while inhibition was 97% with 2 V, and nil with 12 V stimuli. 20 mM calcium depressed noradrenaline release at all applied potentials, and shifted the release versus voltage curve to higher potentials. Manganese (5 mM) and D-600 (10-100 microgram/ml) also considerably inhibited release. This suggests that stimuli of up to 2 V induce transmitter release by exciting intracortical noradrenergic axons in their non-terminal regions.