Cis-dichlorodiammine platinum II (Cisplatin), an effective chemotherapeutic agent, induces acute renal failure by unknown mechanisms. To investigate direct toxic effects of cisplatin on the renal proximal tubular transport system, LLC-PK1 cell line was selected as a cell model and the sugar transport activity was evaluated during a course of cisplatin treatment. Cells grown to confluence were treated with cisplatin for 60 min, washed, and then incubated for up to 5 days. At appropriate intervals, cells were tested for sugar transport activity using α-methyl-D-[14C]glucopyranoside (AMG) as a model substrate. In cells treated with 100 ㄍM cisplatin, the AMG uptake was progressively impaired after 3 days. The viability of cells was not substantially changed with cisplatin of less than 100 ㄍM, but it decreased markedly with 150 and 200 ㄍM. In cisplatin-treated cells, the Na+-dependent AMG uptake was drastically inhibited with no change in the Na+-independent uptake. Kinetic analysis indicated that Vmax was suppressed, but Km was not altered. The Na+-dependent phlorizin binding was also decreased in cisplatin-treated cells. However, the AMG efflux from preloaded cells was not apparently retarded by cisplatin treatment. These data indicate that the cisplatin treatment impairs Na+-hexose cotransporters in LLC-PK1 cells and suggest strongly that defects in transporter function at the luminal plasma membrane of the proximal tubular cells constitute an important pathogenic mechanism of cisplatin nephrotoxicity.