This study was undertaken to determine if susceptibility of cytoplasmically male sterile spring wheat (Triticum aestivum L. em Thell.) to ergot [Claviceps purpurea (Fr.) Tul.] is influenced by pollination and host genotype.Inoculation at various times after hand pollination showed that resistance was established in some lines within a few hours after pollination. The development of resistance after pollination was more rapid in some lines than others, but most lines were nearly immune by 7 days after pollination. Inoculation of diallel crosses between lines that developed resistance quickly after pollination and those that developed resistance slowly indicated that the resistance factor was maternally controlled.