Accelerated PPD-specific proliferation and generation of CD4+ cytotoxic effectors by mononuclear leucocytes (MNL) from tuberculous effusions (EMNL) has been previously reported by our laboratory. In order to explore the contribution of the state of activation of MNL to accelerated reactivity, EMNL and peripheral blood (PB)MNL from seven patients with tuberculosis were assessed both ex vivo and after PPD stimulation. Flow cytometry revealed no difference in the activation state (IL-2 receptor and HLA-DR expression) or cell cycle progression ex vivo. However, CD4+CD29+ memory T cells were accumulated in EMNL compared with PBMNL. In vitro stimulation of EMNL with PPD resulted in accelerated expression of activation markers and progression through the cell cycle (peak after 4 days), whilst PBMNL exhibited normal activation kinetics (peak after 7 days). Accelerated reactivity could not be accounted for by quantitative differences in effusion CD4+CD29+ memory T cells compared with blood, but may be due to a qualitative difference in effusion memory T cells, which are shown to be in a post-activation state of differentiation. T cells entering S and G2/M phases of the cell cycle were largely of the activated memory phenotype. Activation marker expression occurred in association with up-regulation of CD4 antigen expression on the surface of EMNL. Thus accelerated expression of activation markers and cell cycle progression by CD4+CD29+ memory T cells may in part account for accelerated PPD reactivity in tuberculous effusions.