Megasporogenesis and megagametogenesis were examined in a male-sterile, female-fertile mutant (ms1) of soybean (Glycine max (L.) Merr.). Multinucleate (more than eight) megagametophytes resulted from failure of postmeiotic cytokinesis that leads to a coenomegaspore of four haploid nuclei. Fusion of some nuclei may occur. Subsequent development results in mature megagametophytes with up to four eggs, or often abortion. These results support field data that show the male-sterile ms1 gene is associated with increased frequencies of polyembryony, polyploidy, haploidy, and reduced female fertility.Key words: Glycine max, female sterility, polyembryony, polyploidy, megasporogenesis, megagametogenesis.