Initial results are presented on the usefulness of haptoglobin content monitoring in blood serum of patients after thoracic operations performed for various indications. 57 patients were analysed and divided into 3 groups based on the type of disease. Group 1 consisted of patients operated for malignant neoplasm. Group 2 consisted of patients with inflammatory changes and purulent complications within the thorax. Group 3 consisted of patients operated from other indications. The experimental samples of further 30 operated patients have not been analysed yet due to a delay in shipment of plates from Boehringer. The control group consisted of 31 healthy volunteers. In the experimental groups blood was taken 1 day before and 1, 3, 7, 10 and 14 days after the surgical intervention and in the case of complications-21 and 30 days after surgery. Erythrocyte sedimentation, leucocyte level, serum haptoglobin content, clinical and radiological data were analysed. Haptoglobin content was measured using the radial immunodiffusion method according to Manchini. Results were analysed statistically. The increase in serum haptoglobin content in patients after thoracic surgeries and after purulent complications, shows that haptoglobin is a sensitive acute phase indicator and its monitoring may be useful in evaluating the disease process. In advanced neoplastic processes haptoglobin content is a reflection of the progression of the disease process.