Since the invasiveness and metastatic potential of the carcinoma and the proliferation of the tumor cells are the decisional factors in determining the prognosis of carcinoma, it has been a principal area of study to foresee these factors in early stage of the disease process. The purpose of the study was to propose a method to precisely determine the prognosis of tumor. The investigation was performed, using laminin, type IV collagen, and Ki-67 antibody, to reveal the invasiveness and proliferation of the squamous cell carcinoma which is the most prevalent cancer in the area of oral and maxillofacial complex. Frozen tissue sections, 6-8mum in thickness, were prepared from the surgical excision of fresh squamous cell carcinoma for the experimental group. The control group was composed of sections from the normal oral mucosa of the contralateral side. Following incubation in an appropriate primary antibody including laminin, type IV collagen and Ki-67, LSAB method was employed and the tissue sections were treated with DAB for light microscopic immurlohistochemistry. Semiquantitative analysis of the basement membrane was composed of five different positivity of laminin and type IV collagen according to the intensity of the staining. Mean number of Ki-67 positive cells per 2000 total cells in one slide were calculated along with the standard deviation. The obtained results were as follows : 1. In the basement membrane of normal oral mucosa, antibodies against laminin and type IV collagen showed regular thickened, continuous line. Positive reaction was also detected in the vascular walls. Ki-67 labelling index was 4.10+/- 0.80%, and the positive cells were distributed mainly in the basal and parabasal cell layers. 2. In basement membrane of the proliferating tumor adjacent to carcinoma, antibodies against laminin and type IV collagen showed irregular thin, discontinuous line. Ki-67 labelling index was 18.95+/-4.67%, and the parabasal cell layer exhibited increased number of positive cells. 3. In the basement membrane of the main proliferating tumor, antibodies against laminin and type IV collagen showed almost indistinct interrupted line and/or almost indistinct line. Ki-67 labelling index was 31.56+/-5.51%, and the parabasal and spinous cell layer indicated increased cell positivity. 4. Invasive islands showed almost negative reaction to the antibody against type IV collagen, and almost indistinct line of the laminin antibody was observed. Based upon these findings, the loss of laminin and type IV collagen and the Ki-67 labelling index were the highest in the basement membrane of invasive islands. Therefore, it is thought that invasive islands were more deeply involved, than main proliferating tumor, in the invasiveness and proliferation of tumor, and the more the invasiveness of the tumor, the more the cell proliferative activity.