The inability to delay gratification (reinforcement or reward) is one index of impulsive behavior. In order to measure the willingness of pigeons to delay reinforcement, an adjustable delay schedule was developed that allowed daily approximations of an indifference point between immediate brief access to reinforcer and delayed, longer access to reinforcer. Acute administration of the anxiolytic alprazolam (5 mg/kg) decreased the length of delay tolerated before a larger reinforcement. Likewise, acute administration of the anxiolytic chlordiazepoxide (10 mg/kg) produced a similar, although not significant, effect. Neither acute nor five daily injections of 8-OH-DPAT, a 5-HT(1A) agonist, or WAY100635, a 5-HT(1A) antagonist, affected the length of the delay period. Chronic (17 day), but not acute injections of the selective serotonin reuptake inhibitors (SSRIs) fluoxetine (10 mg/kg), citalopram (10 mg/kg) and paroxetine (3 mg/kg) increased the delay period. When given in addition to 1 mg/kg of 8-OH-DPAT, but not 1 mg/kg WAY100635, the effect of fluoxetine was accelerated in that the increase in delay was observed earlier in the treatment. These data support the use of SSRIs to decrease impulsive behavior. Addition of a 5-HT(1A) agonist, but not a 5-HT(1A) antagonist, to the SSRI may hasten the therapeutic activity of the SSRI in treating impulsivity.