The prognostic value of immunophenotyping lymphomas was assessed by studying 51 cases of high-grade non-Hodgkin's lymphoma for which long term clinical follow-up (14-28 years) was available. Using antibodies which identify T- and B-cell-related antigens in formalin-fixed, paraffin-embedded material, 43 were shown to be of B-cell and eight of T-cell phenotype. In terms of survival, cases of high-grade T-cell lymphoma fared significantly worse (P less than 0.05) than cases of high-grade B-cell subtype. These findings support the belief that T-cell lymphomas have a more aggressive clinical course than their B-cell counterparts.