Ascaris suum is an important intestinal nematode causing economic losses in swine. Anthelminthic treatment is used to control A. suum infections and is part of normal production practices. Treatment with anthelminthic agents results in expulsion of adult worms from the intestinal tract and ends further contamination of the environment with eggs. The present study was conducted to determine the effects of drug treatment on the embryonation of A. suum eggs collected from worms obtained from pigs treated with 4 different commercially available anthelmintics. The effects of treatment with abamectin, doramectin, ivermectin, flubendazole, or no treatment on embryonation of A. suum eggs collected from female A. suum expelled in the feces was determined. The embryonation of eggs obtained from pigs treated with abamectin, doramectin, and ivermectin was not significantly (P > 0.05) different from eggs from non-treated control pigs. In contrast, the embryonation of A. suum eggs collected from worms from pigs treated with flubendazole demonstrated inhibited development, and most eggs remained in the 1-cell stage (85.5%) and only 6.3% of eggs developed larvae. In another experiment, we examined the direct effects of doramectin and flubendazole added to solutions of A. suum eggs collected from non-treated control pigs. Egg cultures were exposed to direct in vitro treatment with 0.04-parts per million (ppm) doramectin or 1.0-ppm flubendazole for 24 hr (highest concentrations [Cmax] of drugs in serum) and then embryonation and infectivity for mice was determined. Treatment of eggs in vitro did not significantly effect (P > 0.05) larval development or oral infectivity for mice. Our study demonstrates that flubendazole fed to pigs results in inhibited embryonation of A. suum eggs. However, direct treatment of A. suum eggs in culture for 24 hr with flubendazole did not inhibit embryonation or oral infectivity of in vitro treated eggs. Anthelmintic treatment of pigs in vivo with abamectin, doramectin, and ivermectin had no significant (P > 0.05) effect on embryonation of A. suum eggs, and 24 hr treatment with doramectin in vitro had no direct effects (P > 0.05) on embryonation or oral infectivity of A. suum eggs.