Seventy-one patients with nonsystemic, nonacute glomerulonephritis were included in a follow-up study on the influence of hydrocarbon exposure on the course of their disease. A possible exposure was ruled out by interview performed by occupational hygienists unaware of the outcome of the disease. The patients were allocated to three groups according to their hydrocarbon exposure. One group consisted of patients who had never been exposed; the second of patients who were exposed during follow-up and the third of patients who had discontinued their previous exposure. Each group was subdivided into one group with a glomerular filtration rate (GFR) that remained normal, and one group with a GFR that was, or became, subnormal. Patients with a subnormal GFR who discontinued their exposure had a more favorable course than those who continued to be exposed in spite of an initially lower mean GFR and an initially higher frequency of hypertension. No significant difference was seen between the groups with a normal GFR.