The identification of RET proto-oncogene mutations associated with multiple endocrine neoplasia type 2 (MEN-2) has provided a convenient screening test for MEN-2 in patients with pheochromocytoma (PH). In 120 patients with apparently sporadic PH, we analyzed RET exons 10, 11, 13 and 16 using denaturing gradient gel electrophoresis and found a Leu to Phe missense mutation at codon 790 (exon 13) in 1 case. A TaqI polymorphism located at exon 13 and an AluI polymorphism at exon 14 were present with a similar frequency in the 120 sporadic PH and in 94 unaffected normotensive Caucasian subjects. In 60 patients with PH, including 14 with documented MEN-2, we compared genetic testing with the pentagastrin stimulation test. The latter was 100% sensitive and 92% specific, whereas genetic testing was 88% sensitive and 100% specific. Additional somatic mutations were sought in 35 sporadic PH. Two missense mutations affecting RET exons 11 (C634R) and 16 (M918T) and three neutral mutations at codon 836 of exon 14 associated with the AluI polymorphism were detected. Detection of RET mutations in patients with PH is safe, specific and convenient. Tumoral mutations of the RET gene may play a role in medullary tumorigenesis but seem to be less frequent than previously reported.