In this paper four patients are presented who had been poisoned by 2,4-dichlorophenoxyacetic acid (2,4-D). The first patient, aged 51 years, had attempted to commit suicide by taking orally 400 ml of a 40% solution of 2,4-D. He was admitted in a coma, 6.5 h after poisoning. Extracorporal hemodialysis was performed and the course of the illness was satisfactory. The second patient, aged 80 years, had accidentally drunk 100 ml of a 40% solution of 2,4-D. He was admitted in a coma a few hours after poisoning. Hemodialysis and resin hemoperfusion were performed and the course of the illness was satisfactory. Prior to the above therapy the patient had a 2,4-D serum concentration of 177 mg/100 ml. 2,4-D clearance was 56.3 ml/min during this therapy. The third patient, aged 24 years, had drunk 200 ml of a 40% solution of 2,4-D in a suicide attempt, and paraquat poisoning was also suspected. He was admitted 10 h after poisoning and immediately hemodialysis and hemoperfusion were carried out: the course of the illness was satisfactory. On admittance the concentration of 2,4-D in serum was 122.5 mg/100 ml, and clearance was 72.9 ml/min during treatment. The fourth patient, aged 50 years, had accidentally drunk 100-200 ml of a 40% solution of 2,4-D. He was admitted in a coma 3 h after poisoning. Hemodialysis was performed and the course of the illness was satisfactory. On admittance the concentration of 2,4-D in serum was 37 mg/100 ml and clearance was 68.7 ml/min.(ABSTRACT TRUNCATED AT 250 WORDS)