Abstract: (5.97±0.54)×107 eosinophils per rat were obtained from the peritoneal fluid of P. skrjabini-infected rats forty eight hours after the injection of adult worm extract. Anti-eosinophil serum (AES) was prepared from rabbits immunized by injecting 2×107 rat-eosinophils intravenously four times a month and then bled.Rats were divided into four groups. Animals in the experimental group were administered 1ml AES/100g i. p. every other day for four times. The other three groups of animals were given cortison (Cor), normal rabbit serum (NRS) and normal saline (NS), respectively. Each rat was given 30 cysts of P. skrjabini orally 1 week later. Peripheral blood eosinophils were found to be markedly depressed in AES treated rats. In contrast, eosinophils in NRS-or NS-treated groups increased significantly. The average number and size of worms obtained from the four groups are not significantly different. However, the reproductive systems of the worms in AES-treated rats were well developed, while those in NRS-and NS-treated rats developed poorly, the difference being statistically significant (P0.001).The results suggested that eosinophils might be of importance in inhibiting the maturation of Pagumogonimus skrjabini.