Hodgkin's disease (HD) tumours are characterized by the presence of few tumour cells, the Hodgkin and Reed‐Sternberg (HRS) cells, surrounded by a large amount of non‐neoplastic cells. The role of this cell infiltrate for the development of HD is not known. CD30, belonging to the tumour necrosis factor receptor superfamily, is highly expressed on HRS cells and believed to be involved in tumourigenesis and tumour progression. Tumour samples from 42 patients were immunohistochemically double‐stained for tryptase, a mast cell‐specific proteinase and CD30 ligand (CD30L). Tryptase‐positive mast cells were present in all tumours. Of these cells, 50% expressed CD30L and 66% of the CD30L‐positive cells were mast cells. CD30L mRNA in in vitro developed normal mast cells and malignant human and murine mast cell lines was detected using reverse transcription polymerase chain reaction. CD30L protein expressed on human mast cells was detected using flow cytometry. In a co‐culture assay, the human mast cell line HMC‐1 stimulated thymidine uptake in HRS cell lines, and the stimulation could be blocked using CD30L‐specific monoclonal antibodies. In conclusion, mast cells are present in HD tumours and are the predominant CD30L‐expressing cells. CD30L–CD30 interaction is a pathway by which mast cells may stimulate DNA synthesis in HRS cells.