1. A family is reported with an unusual type of cystinuria.
2. The propositus presented with a cystine renal stone; the renal tubular reabsorption of cystine was grossly abnormal but the tubular reabsorption of ornithine, lysine and arginine was only slightly less than normal.
3. One of the children of the propositus excreted cystine and lysine in increased amounts typical of type II heterozygotes for cystinuria.
4. The renal transport defect in this family may represent one end of the spectrum of cystinuria or it may be a form akin to isolated hypercystinuria.