The influence of 5 mg vitamin B2/100 g b.wt. (B2, riboflavin) on the nephrotoxic effect of 1 or 2 mg Na2Cr2O7/100 g b.wt. (Cr) was investigated in 55- and 10-day-old rats, respectively. Nephrotoxic effect was evaluated by the determination of urinary volume and protein excretion as well as the concentration of blood urea nitrogen (BUN). The concomitant administration of Cr and B2 only in 55-day-old rats increased the nephrotoxicity shown by enhanced proteinuria and BUN. B2, administered 3 h after Cr, was able to diminish Cr nephrotoxicity significantly in 55- and 10-day-old rats. The effect of B2 on Cr nephrotoxicity could be interpreted not by the stimulatory effect of B2 on GSSG reductase, which was abolished by Cr; but by its antioxidant effect.