Glutathione transferase kappa (GSTK1-1) is a highly conserved, mitochondrial enzyme potentially involved in redox reactions. GSTK1-1-deficient mice were generated to further study the enzyme's biological role. Reduced and total glutathione levels in liver and kidney were unchanged by GSTK1-1 deficiency and NADPH quinone oxidoreductase 1 expression was not elevated indicating that there is no general underlying oxidative stress in Gstk1−/− mice. Electron microscopy of liver and kidney showed no changes in mitochondrial morphology with GSTK1-1 deficiency. The death of a number of Gstk1−/− males with urinary tract problems prompted close examination of the kidneys. Electron microscopy revealed glomerular basement membrane changes at 3 months, accompanied by detectable microalbuminuria in male mice (albumin:creatinine ratio of 2.66±0.83 vs 1.13±0.20 mg/mmol for Gstk1−/− and wild-type (WT), respectively, P=0.001). This was followed by significant foot process effacement (40–55% vs 10% for Gstk1−/− and WT, respectively) at 6 months of age in all Gstk1−/− mice examined. Kidney tubules were ultrastructurally normal. Compared with human disease, the Gstk1−/− kidneys show changes seen in glomerulopathies causing nephrotic syndrome. Gstk1−/− mice may offer insights into the early development of glomerular nephropathies.