Low- and high-grade malignant non-Hodgkin's lymphomas have been investigated by immunohistochemistry for their expression of various integrins and CD44 isoforms. Comparison with the expression patterns obtained in non-malignant adult lymph nodes revealed the following differences: alpha 6 and beta 4 integrins were expressed in several high-grade malignant lymphomas to a lower degree than in both the low-grade malignant lymphomas and the normal lymph nodes; all other integrins (alpha 2, alpha 4, alpha 5, alpha v, beta 1, beta 2, beta 3, and beta 7) did not exhibit significant differences in the expression levels between malignant and non-malignant tissues. The standard isoform of CD44 (CD44s) was highly expressed in all lymphoid tissues. Using CD44 exons-specific monoclonal antibodies, CD44 variant isoforms were not detected in non-malignant lymph nodes and were detected only rarely in low-grade malignant lymphomas. In contrast, high-grade malignant lymphomas expressed several CD44 variant isoforms, which included the products from the variant exons 3v, 6v, and 9v, but not 4v. Specifically, detection of exon 3v and 6v products indicates a more aggressive phenotype.