In experiments on female rats the effect of peritoneal dialysis with variously diluted human plasma in peroral poisoning with the organophosphorous insecticide Neguvon, in which inhibition of blood acetylcholinesterase occurs, was examined. Out of the three protein plasma concentrations tested (7 g/l, 70 g/l and 140 g/l), the highest increase in the activity of the inhibited acetylcholinesterase in the blood was induced with the concentration of 70 g/l. A closer examination of the effect of the individual components of the dialysate for Neguvon poisoning revealed that approximately 60% of the effect of treatment is due to albumin, 40% to butyrylcholinesterase in the administered plasma. The comparison of the inhibition of butyrylcholinesterase in the plasma, which was administered as the dialysate, with Neguvon in vitro and in vivo shows that the inhibition of butyrylcholinesterase in the dialysate in vivo is produced by about 35% of the Neguvon dose, administered to experimental animals, and that therefore the actual dose of Neguvon, which induced the poisoning, was decreased to two thirds. This is in agreement with the fact that the LD50 value in treated rats after single-dose administration of the dialysate is more than two times higher than in untreated rats.