Left coronary artery ligation was performed in pentobarbitone anaesthetised rats. Following 1/2 and 2 1/2 h of coronary artery occlusion or sham-operation the right and left ventricular myocardium and the interventricular septum were analysed for tissue content of catecholamines. In control rats and in rats with coronary artery ligation for various time periods (1/2, 2 1/2 and 5 h), the Hillarp-Falck fluorescence histochemical technique was used to visualise the catecholamines of the ventricular myocardium. The tissue noradrenaline content of the left ventricle was markedly reduced after 2 1/2 h of ischaemia while noradrenaline levels in the other parts of the ventricles were unaffected. The adrenergic innervation of the normal rat ventricles is described for the purpose of comparing the normal innervation picture with the appearance after ischaemia. A reduced catecholamine fluorescence was found mainly in the centre of the left ventricular free wall 30 min after coronary artery occlusion. After 2 1/2 and 5 h large areas of the ischaemic myocardium were found to be completely devoid of fluorescent terminals. The border zone between the areas of fluorescence disappearance and normally innervated myocardial tissue was generally quite sharp and occasionally terminals with a diffuse appearance were found in this zone. It is concluded that coronary artery ligation caused a time-dependent loss of noradrenaline from the adrenergic nerve terminals in the ischaemic myocardium. Catecholamine thus released may activate myocardial adrenoceptors and hence be related to increased ischaemic damage and ventricular arrhythmias.