Adult male CD-1 mice were injected with either vehicle or the NK-3 receptor antagonist SB 222200 (2.5, 5 mg/kg s.c.) 30 mins prior to a cocaine (20 mg/kg, i.p.) injection for 5 days. After a seven day drug-free period, all mice were challenged with cocaine (20 mg/kg, i.p.) and behavioral responses were measured. Within vehicle treatment groups, mice injected repeatedly with cocaine had significantly increased ambulatory activity to a subsequent cocaine challenge compared to saline animals indicating a sensitized behavioral response. Administration of SB 222200 blocked this sensitized behavioral response in mice injected with repeated cocaine. Data are presented as mean ± SEM; N=7–12 mice/group (* p<0.05, **p< 0.01).