We have assessed the medium-term effect of a short course of high-dose, alternate-day prednisolone on adult nephrotic patients with membranous nephropathy, using a randomized, prospective, double-blind, controlled trial. Patients were entered over the period 1981 to 1984 and were observed for a minimum of three years. One hundred and seven adult patients who had not previously received immunosuppressive treatment were included in the trial. One hundred and sixty further patients, excluded from the trial, but with membranous nephropathy were identified, followed and assessed retrospectively at the end of the trial. At 36 months there was no significant difference between control and treatment groups in plasma creatinine, creatinine clearance or 24-h excretion of protein. At between three and six months serum albumin concentrations were higher and protein excretions lower in the treatment group compared to controls. No significant benefit was therefore observed on renal function in the medium term.