Patients with adrenal tumors are at risk of the consequences of tumor growth (including metastasis) and of hormone hypersecretion. These tumors arise from tissues with distinct embryonic origins. Pheochromocytomas and paragangliomas arise from the adrenal medulla and produce catecholamines; they may be benign or malignant, and sporadic or familial. Adrenal adenomas and carcinomas arise from the adrenal cortex. Patients with adrenocortical tumors may develop ACTH-independent hypercortisolism, mineralocorticoid excess, and androgen hypersecretion. The tumors are frequently large enough to provide material for biological studies in addition to diagnostic investigations. In France many patients with hypersecretory tumors are referred to the Hypertension Unit of Georges Pompidou European Hospital, and to the Department of Endocrinology at Cochin Hospital, Paris. In 1993, the heads of these departments created the COMETE network (COrtico et MEdullo-surrénale, les Tumeurs Endocrines). The overall objective of COMETE is to promote basic and clinical research into adrenal tumors. This implies - in cross-sectional studies: collecting adrenal tumors, maintaining a collection of tumor and leukocyte DNA samples, keeping a computerized record of relevant biological and clinical data, and distributing biological samples and bioclinical information anonymously to collaborating research laboratories; in prospective studies: ensuring indefinite follow-up of patients with tumors at risk of malignancy or recurrence, which means establishing and maintaining a cohort of patients with large adrenocortical tumors or carcinomas anda cohort of patients with pheochromocytomas or paragangliomas.