To investigate whether atropine is necessary for premedication of flexible bronchoscopy (FFB), 93 patients who underwent bronchoscopy for different indications were randomly separated into two groups. Subjects in the first group were premedicated only with 10 mg of intramuscular (IM) diazepam, whereas the second group was given 10 mg of IM diazepam and 0.5 mg of IM atropine. Blood pressures and pulse rates were recorded before, during, and after FFBs. Blood glucose levels were measured before and after the procedures. Amounts of bronchial secretion and complications related to the procedure were recorded during and after FFBs. The blood pressures were found higher in both groups during the bronchoscopies, whereas only the diastolic blood pressures were significantly higher when compared with the values before FFBs in the atropine-treated group. There was no intergroup difference when increase in blood pressures was compared. The pulse rates were found increased during and after FFBs in both groups (P< 0.05), and the increase in Group II was significantly more when compared with Group I (P< 0.05). Blood glucose levels were measured significantly higher after bronchoscopy when compared with those before the procedure (P< 0.05); however, the increase showed no statistical difference between the groups. Complication rates and amounts of bronchial secretion were similar in both groups of patients. Routine application of atropine for premedication of FFB was found to have no advantages. Instead, it might have some potential disadvantages such as hyperglycemia and tachyarrhythmias in patients with diabetes mellitus and cardiac diseases, respectively.