Studies of peripheral blood lymphocytes (PBL) and plasma from patients with malignant lymphoma [Hodgkin's disease (HD) and non Hodgkin's lymphoma (NHL)] show that plasma soluble interleukin 2 receptor (sIL2R) levels are closely linked with disease status (normal volunteers (n= 15) 402±158u/ml; patients with Hodgkin's disease in remission (n= 4) 525±195 u/ml or with active disease (n= 11) 3026±1602 u/ml (p<0.001); patients with non Hodgkin's lymphoma in remission (n= 6) 462±202 u/ml, active disease (n=15) 2713±1755 u/ml, (p<0.001)) but no correlation between sIL2R and the inhibition of interleukin 2 (IL2) generated cytotoxicity for the cell line K.562. In only 1 of 15 patient plasma samples studied was there a dose dependent inhibition of IL2 generated cell killing. In a further patient, IL2 generated K562 killing was inhibited at all doses (500-3000 brmp units/ml); treatment of this plasma with anti-Interleukin 4 (αIL4) had no effect on the potent inhibitory activity of the plasma. Plasma sIL2R levels were markedly elevated in patients receiving IL2in vivo(pre treatment 520±170iu/ml, during treatment 5578±2564iu/ml,p= 0.05). The aetiology of immunosuppression in patients with lymphoma appears to be multi-factorial; although sIL2R correlates with disease activity it does not appear to directly mediate immunosuppression in most patients with malignant lymphoma.