Basement membrane immunostaining was performed on pepsin-digested, paraffin-embedded blocks of 29 squamous cell carcinomas of the cervix (invasive and in situ) and 13 of the vulva, using polyclonal rabbit antibodies to human laminin and type IV collagen, both staining identically. Laminin with varying defectiveness surrounded invasive foci, whereas adjacent carcinoma in situ or normal epithelium had intact laminin. The amount of laminin usually reflected the degree of tumor differentiation. Absence of laminin around totally keratinized or necrotic tumor nests indicated its dependency on viable cells. New buds from established invasive tumor nests were often more laminin-defective than the parent nest and suggested a cyclic invasive process, with laminin loss during a growth surge followed by laminin reformation during quiescence. In cases of questionable early stromal invasion, deficient laminin could sway the decision toward making a positive diagnosis. The tendency of laminin gaps and tumor buds to contain large malignant cells with pleomorphic nuclei supports the concept of a change in tumor cell metabolism during active invasion. Laminin also appeared around metastatic tumor within lymph nodes. The relationship of inflammation to tumor laminin defectiveness varied.