Albendazole, a benzimidazole anthelmintic, interferes with the formation of microtubules and inhibits meiosis in the nematode Ascaris lumbricoides var. suum. Pigs treated with albendazole had worms in their uteri that had a severely deteriorated central rachis, complete loss of synaptonemal complexes and irregular oocytes at meiotic prophase I. The nuclear matrix and envelope were poorly formed and there was formation of accessory nuclei. This study represents the first examination of the changes in meiotic nuclear architecture and meiotic chromosomes after exposure to albendazole. These results provide the basis for the loss of fecundity in A. suum after exposure to albendazole resulting in control in the population of the parasitic nematode.