Inhibitors of the renin-angiotensin-aldosterone system (RAS) exert beneficial effects in diabetic nephropathy, but the possibility of regression of existing renal lesions remains to be investigated. Teles et al. tested the effects of the RAS inhibitor losartan in rats starting 10 months after induction of diabetes, when glomerular lesions were already present. They linked the reductions of proteinuria with regression of mesangial expansion. More advanced lesions were not affected. There were no dose-response renal effects of losartan.