The effects of administration of phenformin and clofibrate to 32 breast cancer patients who underwent radical mastectomy and suffered from hormonal metabolic disturbances involving a decline in immunologic response were investigated. It was demonstrated that treatment with these drugs during 2–7 months results in an improvement in metabolic parameters and delayed hypersensitivity reaction to DNCB, tuberculin and candidin (75.5% of cases), an increase in T lymphocyte count (56.3%) and an improvement of the reaction of lymphocyte blast transformation (66.6%). The improvement in the immunologic status of the patients persisted for 6–8 weeks after the stoppage of phenformin administration; a gradual decline in immunologic response and return to the original level were recorded 4–6 months after stoppage of phenformin therapy. The effect of clofibrate on metabolic and immunologic parameters did not manifest itself as soon as 6–8 weeks after stoppage. Elimination of metabolic immunodepression, which gradually develops in the course of normal ageing and tumor process, should be the main objective of metabolic immunotherapy. To this end, therapeutic means, other than phenformin and clofibrate, may be used provided they exert the same effects on carbohydrate-fat metabolism. The desirability of study of the effects of a long-term course of drugs of this kind on the therapy of cancer patients is discussed.