The study comprises observations of Se.Cu changes in 29 patients with Hodgkin's disease during treatment with cancertherapeutics and roentgen. It appears that these alterations follow the clinical condition closely, and that they can be used in the evaluation of the therapeutic effect. The alterations are often pronounced and appear early, often they are the first indications of effect. Consequenetly, the Se.Cu determination will be of prognostic value in the treatment. Favourable effect of the applied therapy, with improvement of the clinical condition, is always accompanied by a decrease in Se.Cu. Absence of a fall in Se.Cu during treatment seems definitely to indicate resistance to treatment. Increase in Se.Cu is as a rule accompanied by an aggravation of the patient's condition and by activation of the disease.