1. Serum from patients with fulminant hepatic failure inhibits the ouabain-sensitive sodium efflux in leucocytes. A 1:100 dilution of the serum was necessary before the inhibition became undetectable.
2. Dialysates of the serum through cuprophane in vitro and polyacrylonitrile haemodialysis in vivo were inhibitory in small amounts.
3. Ultrafiltrates (<10 000 daltons) of serum were chromatographed on Sephadex G-25 and the elution profile obtained from patients with fulminant hepatic failure was both qualitatively and quantitatively different from that of normal controls. Material from peaks 3, 4, 5 and 7 in patients with fulminant hepatic failure inhibited leucocyte sodium transport.
4. The dialysate from haemodialysis with the polyacrylonitrile membrane contained most peaks, particularly peaks 4 and 5. Adsorption of serum with polymer coated charcoal in vitro largely removed peaks 5−8.