BACKGROUND: While interruption of angiotensin synthesis and angiotensin blockade are well know to reduce proteinuria and preserve renal function in patients with diabetic glomerulosclerosis, many patients still have significant proteinuria after having reached maximal doses of those medications. We chose to examine the effect of the addition of pentoxifylline to the therapeutic regimen of patients with significant proteinuria and chronic renal insufficiency who had reached maximal does of an angiotensin-converting enzyme inhibitor (ACEI) and an angiotensin receptor blocker (ARB), on the reduction of proteinuria and the preservation of renal function. METHODS: Seven male patients with diabetic glomerulosclerosis with proteinuria of at least 1.5 g/24 hours and a creatinine clearance of at least 15 ml/min despite maximal doses of an ACEI and an ARB for over 12 months were treated with pentoxifylline adjusted for creatinine clearance. They were then compared with 7 similar patients matched for age, duration of medications, proteinuria, creatinine clearance and mean arterial pressure. The groups were compared for any significant differences on at baseline and at 12 months. RESULTS: Although proteinuria decreased in the pentoxifylline group (5.657 +/- 3.5227 to 3.799 +/- 3.647 g/24 hours) there was no significant difference from the control group (4.743 +/- 2.320 to 4.986 +/- 2.941 g/24 hours). Similarly both groups lost creatinine clearance (41.0 +/- 27.44 to 29.33 +/- 22.21 ml/min with pentoxifylline and 45.57 +/- 21.854 to 27.33 +/- 27.105 ml/min in controls), but there was no significant difference in either clearance or mean arterial pressure. CONCLUSION: Although there was a trend toward the reduction of proteinuria, we found no statistical benefit in proteinuria reduction or preservation of renal function by the addition of pentoxifylline to maximal doses of ACEIs and ARBs.