Free plasma DNA was extracted and terminal restriction fragment (TRF) sequences were amplified by polymerase chain reaction in 32 patients with stage 3 and stage 4 ovarian cancer and 45 healthy controls. Three peaks of TRF were identified and the size of the largest peak (peak 1) correlated with cancer telomere length in cancer patients. Average size of peak 1 in cancer patients was significantly shorter than in controls. When plasma TRF peak 1 was tested pre- and post-treatment, the average pre-treatment size was 8.7 +/- 0.5 Kb, lengthening significantly post-treatment. In long-term survivors of ovarian cancer (10-year disease-free survival), plasma TRF length was the same as in normal controls. The results suggest that the plasma TRF in ovarian cancer patients is of tumour origin. Its determination may reflect tumour cell viability in the host.