The ultrastructural morphology of the hemidesmosomes in malignant epithelial cells of invasive squamous cell carcinoma of the human larynx was studied by electron microscopy. In the more advanced carcinomas the hemidesmosomes are reduced in number or absent over extensive areas of the epithelial stromal junction. In some places the hemidesmosomes are observed to be in the process of being dislodged from their normal sites at the plasma membrane of the basal carcinoma cell. After dislodgment from the basal plasmalemma into the subepithelial connective tissue the hemidesmosomes are seen to round off with the cytoplasmic attachment plaques lying on their inner circumference. A constant feature of the detached hemidesmosomes is the absence of inserting tonofilaments. Frequently, the detached hemidesmosomes are found to be in close association with detached multilayered basement membrane material in the stroma. The detached hemidesmosome-structures appear to migrate down into the deeper layers of the connective tissue space apparently loosing their distinct ultrastructure. These observations indicate that the detachment of hemidesmosomes and their subsequent downward dermal migration may result in a loss of epithelial-stromal adherence in invasive epithelial cancer of the larynx.