The influence of metabolic control and blood pressure on the onset and course of clinical nephropathy (persistent proteinuria) was investigated in 63 type II diabetics with persistent proteinuria and a corresponding group without proteinuria. Diabetics with a later onset of persistent proteinuria had, even in the pre-proteinuria stage, higher blood pressures than diabetics without proteinuria. There was an inverse relationship between blood pressure and the interval between the diagnosis of diabetes and the onset of persistent proteinuria. There was no difference in metabolic control between diabetics with and those without later development of persistent proteinuria. However, for patients with clinical nephropathy there was a weak inverse correlation between blood pressure levels during the preproteinuric stage, on one hand, and the interval between diabetes diagnosis and onset of persistent proteinuria, on the other. Poor metabolic control and hypertension during the proteinuric stage were associated with rapid deterioration of renal function.