The diagnosis of iminoglycinuria was established in two patients on the basis of increased urinary excretion of proline, hydroxyproline and glycine in the presence of normal plasma concentrations of these respective compounds. Routine metabolic screening was performed in these infants in order to find the cause for the developmental delay observed in one infant and the siblings deaths noted in the family of the other. These two patients gave further support to the previous suggestion that renal iminoglycinuria is a benign disorder with no recognizable clinical pattern. Its detection, therefore, requires screening programs or amino acid studies.