Tissue from 86 cases of Hodgkin's disease, fixed in formalin and embedded in paraffin, was immunostained for the T-cell marker CD3. Of these cases, 20 were selected on the basis of previous reactivity of Reed-Sternberg cells for T-cell associated antigens in frozen sections whilst the remaining 66 were retrieved from the routine pathology files. Five of the 20 selected cases and 22 of the retrieved cases showed predominantly cytoplasmic positivity in a subpopulation of Hodgkin and Reed-Sternberg cells. CD3 positive cells were present in all subtypes of Hodgkin's disease including three of nine lymphocyte predominance cases. It therefore appears that some Hodgkin and Reed-Sternberg cells can express the major T-cell antigen CD3. Although these findings are open to other interpretations, they are consistent with the hypothesis that at least some cases of Hodgkin's disease arise from activated T-cells.