The family of CD44 glycoproteins has diverse functions in cell-cell and cell-matrix interactions. The standard form of CD44 is of importance in the dissemination of lymphoma, whereas the clinical significance of the variant exon v6-containing forms of CD44 (CD44v6) is not known. The expression of different forms of CD44 was investigated by using antibodies against the constant part of CD44 (CD44c) and CD44v6 in 56 primary and 17 recurrent non-Hodgkin's lymphomas and correlated with several clinicopathological parameters and with prognosis. Fifty-seven per cent of the primary non-Hodgkin's lymphomas expressed CD44v6 and 73 per cent expressed the constant epitope. Expression of both CD44c and CD44v6 was associated with low histological grade of malignancy. CD44c expression was associated with a low cellular proliferation rate as assessed by DNA flow cytometry. Of several factors tested, high expression of the variant from v6 was the only factor that was associated with unfavourable recurrence-free survival (P = 0.04). We conclude that CD44v6 is associated with a low histological grade, but, on the other hand, with an unfavourable outcome, which suggests that the combination of CD44v6 and histological grading may form a particularly strong prognostic parameter in non-Hodgkin's lymphoma.