Oral squamous cell carcinomas were studied in regard to lymph node metastasis (LNM). Relations between LNM and the mode of cancer cell invasion, basement membrane (BM) deposition, epidermal growth factor-receptor (EGF-R) on tumor cells, stromal lymphocyte infiltrates, and immunologic parameters such as natural killer (NK) and interferon (IFN) activity were investigated. In 76 carcinomas, 26 cases (34.2%) exhibited LNM. LNM was rare in limiting invasion type (grade 1 and 2), but LNM was occasional in grade 3 invasion (11/29), and extremely prominent in diffusely invasive type of grade 4C and 4D (6/10 and 4/5, respectively). Tumors showing sufficient BM deposition were poorly metastatic (only 5 tumors had positive lymph nodes in 30 cases showing sufficient BM deposition which was immunohistochemically delineated with type IV collagen), while tumor having limited BM deposition were highly metastatic (12 in 16 tumors). Weakly infiltrated carcinomas with Leu 2a+ cells exhibited generally limited laminin existence in BM, and these carcinomas were more metastatic. Furthermore, EGF-R was more expressed on tumor cells with LNM than cells without LNM. There was no significant differences between NK activities of patients with LNM (32.9 +/- 18.3%) and without LNM (37.2 +/- 16.3%). Cases having activities of less than 17.2% (mean-2SD in healthy controls) were more frequent in metastatic group (7/19) when compared with non-metastatic group (4/33). IFN activities in sera were significantly different between metastatic group (4.2 +/- 3.1 IU/ml) and non-metastatic one (9.5 +/- 7.0 IU/ml. From the above, LNM may be more accurately diagnosed by these immunologic investigations.