The use of progestagenic hormones in the treatment of endometrial carcinoma is reported in this paper. Optical microscopy and ultrastructural techniques used in morphological investigation established extremely good response to treatment primarily by adenocarcinomas which are characterised by advanced histologic differentiation. Deceleration of tumour progression was a clinical result of the therapeutic approach taken, with shorter or longer periods of remission being recordable. The results are likely to support the assumption that "cytostatic" action of progestagenic substances can yield desirable complementary effects in cases when surgical or radiological treatment is abandoned for high risk.