Twenty-two patients with histologically demonstrated diffuse proliferative lupus nephritis (DPLN) and glomerular thrombosis received a 14-day course of ancrod, followed in most by nitrogen mustard (mechlorethamine hydrochloride) 0.4 mg/kg. Many were referred when renal function was deteriorating despite large doses of prednisone. The patients had severe disease; there was a high degree of glomerular sclerosis; the median serum creatinine was 137 mumol/l, the diastolic blood pressure 101 mm Hg. Reported previously was a short-term improvement in renal function, blood pressure, and renal histology. Reported here is the long-term follow-up on all 22 patients for an average of 58 months. Three died of causes other than renal failure. Eleven developed end-stage renal disease an average of 27 months after ancrod treatment. The other 8 are alive with no deterioration of renal function after an average of 70 months. This outcome seems satisfactory when disease severity is taken into consideration. Factors present at treatment start that might be associated with subsequent renal function deterioration were: prior prolonged prednisone treatment, extensive glomerular sclerosis, high plasma alpha 2-antiplasmin and possibly triglycerides. During the follow-up period after completion of treatment, later relapses of SLE and DPLN appeared to be an important predictor of deterioration of renal function.