We studied the effect of lysosomal loading with cystine (by incubation with cystine dimethyl ester, CDME) on the functions of renal epithelial cells in culture (LLC-PK1). The concentrating capacity (the ratio of the intra- and extracellular concentrations) of the nonmetabolized glucose analog, α-methylglucoside (AMG), was reduced after incubation with CDME in a dose- and time-dependent manner. Consistent with these findings was a 30% reduction in the number of the sodium-coupled D-glucose transporters assessed by phlorizin binding. Since the impairment in glucose transport was less effective with other amino acid methyl ester analogues, LLC-PK1 cells treated with CDME can be used to study the cellular mechanisms responsible for the impairment of kidney function in cystine accumulation diseases, e.g., cystinosis.