Background: Optimal cytoreduction is a major prognostic factor in ovarian cancer; several clinical, radiological and biochemical predictors have been studied. Tumour M2-PK (TU M2-PK) is over-expressed in tumour cells and can be detected in plasma samples but its role in ovarian cancer has not yet been evaluated. Objectives: To assess the potential clinical applications of TU M2-PK in ovarian cancer particularly in relation to surgical cytoreduction. Settings: The Gynaecological Cancer Centre at both King's College and St Thomas' Hospitals; London; UK. Methods: Patients with suspected ovarian cancer were recruited prospectively during the years 2004-2005. Blood samples were collected before surgery for plasma TU M2-PK assays. Data were analysed in relation to cancer diagnosis and outcome. Statistical analysis was performed using Analyse-It® and SPSS® Vl3. Results: 100 patients were recruited; 52 diagnosed with invasive ovarian cancer, 13 with borderline tumours and 35 patients had benign conditions. The mean M2-PK concentration in cancer patients was 52 U/ml vs 31 U/ml in patients with borderline tumours and 22 U/ml in those with benign conditions (p < 0.001); it was significantly raised in association with late stage disease and higher grade (p < 0.05). Taking 35 U/ml as a reference point, TU M2-PK predicted sub-optimal cytoreduction in advanced stage disease with a sensitivity of 69%, specficity of 60% and overall efficacy of 61 % (95% CI: 44-75%). Conclusion: TU M2-PK was significantly raised in ovarian cancer patients, particularly those with higher stage disease. The potential clinical application as a predictor of surgical outcome in ovarian cancer needs further evaluation.