After operations conducted for malignant gynecological tumours the changes in serum proteins and their spectra had in the main the same pattern as after operations indicated for diseases of a benign character. 2. The changes took place however at a markedly lower proteinemia level and issued from values occasinally strikingly affected by the presence of the malignant tumour. 3. A particular phenomenon was the presence of changes in the concentration of the electrophoretic gamma-globulin fraction which showed, in cases of advanced ovarian tumour, a rapid increase during the first postoperative days. 4. The changes in serum proteins found after operations made for malignant tumours were less regular and took place in some cases in form of irregular oscillation.