The detection of tumor-specific T cells in immunized cancer patients usually relies on lengthy and difficult CTL assays; we now report on flow cytometry to detect the intracellular cytokines interleukin 2 (IL-2), IL-4, IFN-gamma, and tumor necrosis factor alpha (TNF-alpha) produced by CD4+CD69+ and CD8+CD69+ activated T cells after MUC1 antigen stimulation. Peripheral blood mononuclear cells were obtained from 12 patients with adenocarcinoma injected with mannan-MUC1; cells were exposed in vitro for 18 h to MUCI peptide in the presence of CD28 monoclonal antibody and Brefeldin; permeabilized cells were used for the expression of cytokines. After stimulation in vitro with MUC1-variable number of tandem repeats peptides, CD8+CD69+ T cells from all immunized patients generated 3-9 times higher levels of TNF-alpha(P < 0.038) and IFN-gamma (P <0.010) than did cells from 12 normal subjects; minor increases in IL-4 occurred. By contrast, CD4+CD69+ cells showed no overall alteration in TNF-alpha and IFN-gamma cytokine production, although in some patients, their measurement was informative; the measurement of IL-2 was not useful in either CD4+CD69+ or CD8+CD69+ cells. We conclude that in MUC1-immunized patients, the measurement of TNF-alpha and IFN-gamma in activated CD69+CD8+ T cells may be indicative of their immune status.