In a prospective, placebo-controlled, double blind trial patients with moderate impaired kidney function receiving hypoosmolar, nonionic contrast medium were randomly assigned to an oral treatment for 2 days with 1.2g/day of NAC (n=19), for 1 day with 60mg/day of Zn (n=18) or placebo (n=17). All patients were periprocedural hydrated with 1ml/kg/h of 0.45% saline for 24h. At baseline (before hydration), prior to exposure of CM as well as 2 and 6 days after CM serum levels of creatinine and cystatin C have been measured.