The present study examined the role of noradrenaline (NA) in the central nucleus of the amygdala (cA) in the sensitization of the acoustic startle response (ASR) in rats. In the first experiment, local microinjections of 0, 0.5, 1, 2 nmol of the alpha 2-adrenergic antagonist yohimbine into the cA increased the magnitude of the ASR in a dose-dependent way. In the second experiment, foot shocks were applied to increase the ASR amplitude (sensitization). Local microinjections of 0, 4, 8, 16 nmol of the alpha 2-adrenergic agonist ST-91 into the cA dose dependently decreased the sensitizing effects of foot shocks on the amplitude of the ASR. It is conjectured that yohimbine increases and ST-91 decreases local NA release by acting at presynaptic autoreceptors. The present data suggest that the release of NA in the cA is involved in the mediation of the sensitizing effects of foot shocks on the ASR.