The feasibility and safety of thallium-201 myocardial scintigraphy after the intravenous infusion of adenosine triphosphate disodium (ATP) (Adetphos, Kowa) were studied in eight patients with angina pectoris and/or old myocardial infarction. Coronary arteriography (CAG) was performed by the conventional method in all patients. ATP was infused for 5 min and thallium was injected at 3 min after the start of ATP infusion. ATP was given at 0.12 mg/min/kg in two patients (group A), 0.16 mg/min/kg in three patients (group B), 0.20 mg/min/kg in one patient (group C) and 0.28 mg/min/kg in two patients (group D). SPECT images were obtained at 10 min and 180 min after thallium injection. No significant hemodynamic changes were observed in group A and B. Severe hypotension was observed in group C and one member of group D. Chest pain was experienced by one patient in group A, two in group B, one in group C, and both of the two in group D. ST depression on the electrocardiogram (ECG) was documented in one patient each of groups B and C. In one group D patient, the study was discontinued because of complete atrioventricular block persistent for 5 beats. The correlation between thallium imaging and CAG was unclear in group A, reasonable in groups B and C, and obscure in group D because of side effects. None of the patients who developed side effects of ATP were administered sublingual nitroglycerin or intravenous aminophylline. Their symptoms or ECG changes improved spontaneously within 2 min and disappeared within 5 min after termination of infusion. In conclusion, the optimal ATP regimen for this purpose was considered to be a 5 min infusion at 0.16 mg/kg/min and this method was found to be feasible and safe.