Non-insulin-dependent diabetes mellitus (NIDDM) may be the most rapidly-growing chronic disease in the world. Its long-term complications, including retinopathy, nephropathy, neuropathy, and accelerated macrovascular disease cause major morbidity and mortality. Although therapy that normalizes glycemia may prevent the development and delay the progression of long-term complications in NIDDM, as has been demonstrated in insulin-dependent diabetes mellitus (IDDM), no direct data exist to support the efficacy of "intensive therapy" in NIDDM. An alternative approach to preventing the development of long-term complications may be to intervene more distally, i.e., inhibit the mechanism(s) by which elevated glucose levels cause complications. Potential pathogenic mechanisms include the accumulation of sorbitol and other biochemical changes in tissues with aldose reductase, and the modification of proteins by glycation. Pharmacologic probes, including aldose reductase inhibitors and glycation inhibitors such as aminoguanidine, are currently under study and may provide an efficient means of preventing complications, independent of the ambient glycemic level.