A cervical factor accounts for 5% to 10% of infertility among women. In the absence of an immunologic or endocrine-related basis for incompetent sperm/mucus interaction, an idiopathic cause is usually ascribed. This study describes quantitative analyses of the microstructure of mucin strands, observed under scanning electron microscopy, from infertile women displaying incompetent sperm/mucus interaction unrelated to any apparent immunologic or endocrine-associated cause. The results revealed a highly significant reduction in the spacing of mucin fibers incompatible to sperm penetrability and migration. Additional quantitative measurements of mucin strand diameter and number and geometry of strand crosslinks suggest inadequate hydration of the mucin gel as a causative basis for the structural inadequacies observed in some cases of cervical-factor infertility.