We report on the cases of two patients referred for 131I treatment of hyperthyroidism who were dependent on haemodialysis. Following 131I administration, all disposable lines and filters from dialysis were collected and measured for 131I radioactivity. The amount of 131I retained by the filters at the end of each successive dialysis session was found to decay with effective half-lives of 6.6+/-0.2 and 6.3+/-0.2 days. Dose rate measurements at 1m from the patients were recorded to find the effective half-life of the radioiodine clearance, which were found to be 6.9 and 7.1 days. From measured dose rates taken at 30 cm, the radiation hazard to ward staff involved in patient management was shown to be negligible.