Non-dextran intravenous (i.v.) iron preparations seem to differentially affect proteinuria in patients with chronic kidney disease. To study effects of ferric gluconate and iron sucrose on proteinuria, we conducted a crossover trial in 12 patients with stage 3-4 chronic kidney disease. These patients were randomized to receive the same dose of either drug 1 week apart. Urine samples were obtained immediately before and at frequent intervals after the drug. The urine total protein/creatinine ratio was significantly greater after iron sucrose than ferric gluconate treatment with the effect noted within 15 min post-infusion. Furthermore, when iron sucrose was given first, a significantly greater protein/creatinine ratio was seen subsequently with ferric gluconate than with the reverse order of treatment. The urine albumin/creatinine ratio was also significantly greater with iron sucrose than with ferric gluconate. There was no significant difference, however, between the two i.v. irons in the measured urine N-acetyl-beta-D-glucosaminidase/creatinine ratio. Although our study showed that acutely, iron sucrose increased proteinuria, the long-term effects of repeated i.v. non-dextran iron on kidney function requires further study.