OBJECTIVE This study was performed to examine possible use of thymidine kinase 1 concentration in serum (STK1) for prognosis of non-Hodgkin's lymphoma patients following chemotherapy treatment. METHODS The STK1 levels of 37 patients were determined by enhanced chemiluminescent dot-blot assay on the day before chemotherapy, and on day 1 and day 28 after start of the treatment. The specificity and sensitivity was evaluated by Western blot with anti-TK1 IgY antibody and by receiver operating characteristic (ROC) analysis. RESULTS Western blot and ROC analysis of TK1 in serum showed high specificity and sensitivity. The mean STK1 level of the non-Hodgkin's lymphoma patients was significantly higher compared to healthy persons (p < 0.001). The mean STK1 level increased significantly (p < 0.001) on day 1 and then declined, reaching on day 28 values corresponding to those of healthy persons. The mean STK1 values before treatment and at 1 and 28 days after start of the treatment also correlated significantly with the clinical response (CR, PR and NR) and five-year survival. CONCLUSIONS Although the number of patients was limited in this study, TK1 in serum might possess an important reference value in the evaluation of treatment and prognosis of non-Hodgkin's lymphoma following chemotherapy.