Tryptase is the most abundant protease in human mast cells, and is often used as a marker for the enumeration of mast cells in tissue. Here we report that tumour cells from Hodgkin lymphoma, the so called Hodgkin and Reed-Sternberg cells, can express tryptase. Hodgkin lymphoma cell lines expressed mRNA for both alpha- and beta-tryptase and also produced the protein, although at much lower concentrations than mast cells. However, the frequency of tryptase positive HRS-cells in situ was very low. This report demonstrates that tumour cells of lymphoid origin can express tryptase in vitro and in situ.