Methods The first kidney was surgically removed from a 35-yr-old woman with left kidney carcinoma. There was a positive family history: the mother died at age 53 from polycystic kidney disease; and one sister, a great-uncle, and a cousin were similarly affected. In this family, death from renal insufficiency occurred between 40 and 50 yr of age. At the moment of nephrectomy, renal function was still satisfactory (creatinine clearance, 118 mI/mm). The radiologic diagnosis of carcinoma in a cystic kidney was made at the time of exploration for hematuria. The left kidney was palpable. During the operation, the slightly enlarged kidney was removed (total weight, 300 g after fixation in 10% formalin). After stripping off the fibrous capsule, multiple cysts containing transparent fluid were exposed (Fig. 1.) Their maximum diameter was 2 cm. The pelvis and ureter were normal. The diagnosis of clear-cell carcinoma in the lower pole was confirmed histologically. Wedge-shaped pieces of tissue, not more than 2 mm in thickness, were cut from the coronally bisected kidney to include the cortex and medulla in continuity. A number of representative samples from different lobes of the kidney were taken for microdissection. The second patient was a 33-yr-old woman, on whom we operated for a large stone in the intrarenal pelvis. There was a positive family history of poly-