We have introduced behavior therapy as standard in-patient treatment for anorexia nervosa and have modified the treatment program. At first, we used Fukamachi's activity restriction therapy (FT), followed by Token economy therapy (TET), which combined token economy with FT. Finally, we have developed Kyoto Prefectural University of Medicine Behavior Therapy (KPT). According to KPT, only liquid formula is given in the early stages of hospitalization and a target weight is not set at admission. We examined the effect of these three programs with respect to bodyweight gain. Thirty-five anorexic patients participated in these three programs in our hospital: seven completed FT, seven completed TET and 21 completed KPT. We compared the effects of these three programs on body mass index (BMI). Furthermore, the effects of these three programs on BMI were compared at admission, 1 month after admission and at discharge, 6 months after discharge. In addition, the rate of increase of BMI for the following three periods was investigated: 1 month after admission, total hospitalization (from admission to discharge) and from admission to 6 months after discharge. The result is that KPT was the most effective of the three programs with regard to both the amount and the rate of increase of BMI at all points and there is a significant difference between KPT and FT. This effectiveness may be attributable to the use of an oral liquid formula, the setting of target weight at a later stage of hospitalization and the release of activity restriction based on weight gain.