In a retrospective study of 31 patients with suspected pheochromocytoma we examined the preoperative results of 131I-metaiodobenzylguanidine (131-I-MIBG) scintigraphy and a fluorimetric urine catecholamine determination test. An additional radioenzymatic plasma catecholamine determination test was performed in 25 patients. In 14 of the 31 patients the diagnosis of pheochromocytoma was later histologically confirmed. In the remaining 17 patients the suspected diagnosis was finally rejected after a clinical decision had been made on the basis of clinical history, symptoms, laboratory and imaging tests. 131-I-MIBG scintigraphy apparently had a very high specificity (no false-positive results among the patients with rejected diagnosis), but showed the least sensitivity (3 of 14 tumours were not detected). Urine catecholamines showed two false-negative and three false-positive results. Plasma catecholamines had the highest sensitivity and gave only one false-positive result. Because of its high pathognomonic value 131-MIBG scintigraphy can be helpful not only for localization, but also for confirmation of diagnosis when catecholamine determination tests are contradictory. On the basis of our experience with false-positive results after interfering medication therapy, urine and plasma catecholamine determination tests should only be carried out after purification with thin layer chromatography or high performance liquid chromatography.