We compared bcl-2 with P-glycoprotein expression (C494 and JSB1), and both with ex vivo chemosensitivity by Differential Staining Cytotoxicity (DiSC) assay (25 cytotoxic drugs), in 76 fresh haematological specimens, including 51 chronic lymphocytic leukaemias (CLL). Strong correlations were seen between bcl-2 and Pgp expression in both CLL (r = 0.5; p < 0.001) and AML (r = 0.9; p < 0.001) although bcl-2 expression was only raised in Pgp positive cells. However, there was no correlation between high or low marker levels and either ex vivo drug sensitivity (-0.30 < r < 0.37; p all > 0.1) or patient survival (chi 2 < or = 0.1; p > 0.7). One B-CLL, one PLL and one hairy cell leukaemia were negative for both bcl-2 and Pgp, whilst 3 T-cell specimens were bcl-2 negative but strongly positive for Pgp. These results suggest that the expression of Pgp and bcl-2 may be interlinked and related to immunophenotype and that clinical sensitivity to MDR-inducing and/or apoptosis-inducing drugs is best determined by ex vivo chemosensitivity testing rather than measurement of Pgp or bcl-2 expression.