We evaluated the safety and stability of balloon infusors in which the distended elastomotor balloon acts as the energy source. Continuous intravenous administration of 5-fluorouracil with the infusor was carried out in nine patients with advanced gastrointestinal cancers. In additional two patients, morphine hydrochloride was administered continuously in the vein or in the epidural space. The patients were carefully observed and hematological and biochemical examinations were performed. Infusion volume was calculated by measuring the weight of the infusor. The present study showed that this infusor was safe and easy to handle. However, the infusion velocity was slightly unstable, being influenced by the temperature of the infusor. This infusor was used even on an ambulatory basis. According to our results, we thought this infusor is quite useful to improve the quality of life of cancer patients.