T cell receptor gamma delta+ (TCR gamma delta+) cells are present in all lymphoid tissues, but at lower frequencies than TCR alpha beta+ cells. In normal spleens, they account for about 15-20% of CD3+ cells. In hairy cell leukemia (HCL), a B cell malignancy with a characteristic involvement of the spleen, splenic T cells of approximately 40% of the examined patients showed a remarkable increase in CD3+ TCR gamma delta+ cells. Therefore, we studied the TCR gamma delta phenotypes in blood and spleen of 12 HCL patients in comparison with normal samples. In normal blood (n= 6) the majority of TCR gamma delta+ cells expressed the Vgamma 9V delta2 phenotype, while in normal spleens (n = 9) a different population was found expressing Vdelta1. In contrast, six of eight paired blood and spleen samples of individual HCL patients demonstrated the same phenotype with predominantly Vgamma 9V delta2 expression. This change in splenic TCR gamma delta usage in patients with HCL might be the result of cell-trapping, or an infiltration of TCR gamma delta+ cells from the blood.