An observational study on the role of Doppler sonography in the assessment of patients with malignant trophoblastic disease was performed in an Oncology Unit of a University teaching hospital. A total of 32 consecutive patients referred for chemotherapy were recruited. Twenty-three non-pregnant and 18 women in the first trimester of pregnancy acted as controls. The patients were prospectively followed-up for 2 years. It was found that the uterine arterial resistance index and pulsatility index in patients who required chemotherapy were significantly lower when compared with the non-pregnant and pregnant controls; (Student t-test; P < 0.001 and P < 0.01, respectively). Stepwise regression analysis of beta-hCG titres on uterine artery resistance index showed significant correlation, after controlling for uterine volume (adjusted multiple R = 0.71, P < 0.00001). There were, however, no significant independent associations between the initial uterine artery resistance index and the need for chemotherapy, number of courses of chemotherapy required, duration required for the beta-hCG titre to return to normal, presence of metastatic disease, or the subsequent development of drug resistance or relapse. It was concluded that uterine arterial Doppler indices are significantly correlated with trophoblastic activity (beta-hCG titres) in malignant trophoblastic disease. However, their role in the prediction of subsequent tumour behaviour need to be assessed in larger series.