The work aimed at the establishment of the ovostatic action of Na₂HP³²O₄, dilombrine and piperazine on the eggs of Ascaris suum. The eggs were placed in Barbagalla fluid, 4 ml in each tube, with the density of 10000 eggs/1ml at the temperature of 26°. To the tubes with egg suspension was added radioactive Na₂HP³²O₄ at various concentrations so as to obtain radioactivity in the concentrations of (I) 1.5 μC/ml, (II) 3 μC/ml, (III) 4.5 μC/ml. Dilombrine, at the concentration of 0.1 mg/ml, 0,0l mg/ml and 0.001 mg/ml was added to one series of tubes with P³², and piperazine at the concentration of 20 mg/ml to the other series containing P³². The experiments demonstrated that P³² at the given concentrations did not affect essentially the development of eggs. A considerable inhibition in the development of eggs could be seen in tubes with dilombrine and it was proportional to the concentration of the drug. In tubes with piperazine solution there was also an inhibition in the development of eggs. The P³² cumulation in eggs placed in piperazine solution was at first 10 times less than in Na₂HP³²O₄ solution and a few times lower than in dilombrine solution.