OBJECTIVE Several abnormalities of the T-cell receptor (TCR) CD3 transduction pathway in cancer patients including B-cell neoplasms have been reported. Adequate activation of the receptor is important to provide stimulus for the T-cell to start its effector functions. Activation of TCR/ CD3 results in recruitment of tyrosine kinases and changes of tyrosine phosphorylation levels. We investigated phosphorylation levels in T-cells from multiple myeloma patients at diagnosis and compared them to normal individuals. METHODS We quantitatively analyzed protein phosphorylation of resting and anti-CD3 stimulated Tcells in 10 previously untreated multiple myeloma patients and 6 healthy donors using two-colour flow cytometry. The results were shown as a median fluorescence intensity values. A specific monoclonal antibody directed against phosphotyrosine was used. RESULTS No significant differences between helper Tcells and cytotoxic T-cells and no significant differences between multiple myeloma patients and controls were found. CONCLUSIONS The flow cytometry technique used in our experiment allows a quick insight into phosphorylation pattern following activation of T-cells. Further experiments combining this method with measuring the activity of particular tyrosine kinases of the activation cascade may bring the necessary information explaining the nature of T-cell dysfunction.