In a retrospective survey of patients who have had a proven attack of acute intermittent porphyria (AIP) in the West of Scotland a highly significant association (p less than 0.001) was observed between AIP and the development of early-onset chronic renal failure. Six patients with AIP and chronic renal failure arising in early middle-age are described. As no other cause could be attributed to the renal failure three possible causal links between these two conditions were considered, namely, enhanced susceptibility to analgesic nephropathy, porphyria-induced hypertension, and nephrotoxic effects of porphyrins and their precursors. We suggest that porphyria-induced hypertension is the most important factor in causing early-onset chronic renal failure in acute intermittent porphyria.