The effects of an 'anorectic' drugs as an adjunct to a behavioral weight-loss programme were investigated. Four groups of 20 began an initial two weeks of instruction. Groups 1, 2, and 3 were instructed in a behavioral programme utilizing a food diary, stimulus control techniques, and reinforcement. Group 4 was instructed in a relaxation programme. Group 1 took phentermine resin 30 mg for eight weeks, followed by a placebo for eight. Group 2 took placebo for eight and phentermine for eight. Group 3 took placebo for 16. Group 4 took placebo for eight and phentermine for eight. All groups were followed for an additional eight weeks. A significant number of subjects in all behavioral groups achieved some weight loss. (A significant difference among the mean percentage body weight reduction for the three behavioral groups was also found.) In addition, a group of 'slow losers' who initially lost less than one half-pound (0.2 kg) per week and were subsequently placed on phentermine lost significantly more weight than a similar group which continued on placebo. These differences were maintained for 24 weeks.