A free-floating rubber balloon was installed as an artificial intragastric bezoar in five obese women. These patients were studied for a total of 272 days - i.e., 130 days with the balloon inflated (10 periods) and 142 days when the balloon was known to be deflated (7 periods). The balloons were easy to insert and reduced hunger. They remained inflated for 7 to 21 days (median 12 days) as judged by radioscopy. Collapsed balloons passed unnoticed with the stools. There were no complications associated with their use. During consecutive periods with balloon, without balloon, and with balloon average weight-losses over 10 days were: 5.0 kg (range 8.6 to 2.0), 0.5 kg (2.9 to 0.3), and 2.1 kg (2.6 to 1.2), respectively. The weight-loss observed while the balloons were inflated is promising but the efficacy of the method can only be evaluated when balloons which remain inflated for several months within the stomach become available.