A patient suffering from recurrent leg ulcers excreted large amounts of iminodipeptides in the urine. Among the iminodipeptides excreted, Glu-Hyp, Asp-Pro, Glu-Pro, Leu-Hyp, Gly-Pro, Thr-Pro, Ser-Pro, Ala-Pro, Val-Pro, Ile-Pro, Leu-Pro and Phe-Pro were identified and their quantities estimated. Some of the iminopeptides were synthesized for identification.