Two and three Dow Cordis Hollow Fiber and Gambro Lundia artificial kidneys were used for high efficiency dialysis in large patients, intoxications, and for rapid ultrafiltration. BUN clearances of up to 240 ml/min were achieved. One episode of severe neuropathy occurred during high efficiency dialysis, and hypotensive episodes were more common. High efficiency dialysis has certain indications particularly in intoxication cases. However, because of possible side effects more experience is needed before its ultimate place in the treatment of uremia can be ascertained.