SB-334867 is a selective antagonist of orexin-1 receptor . Orexin-A and orexin-B are two peptides isolated from rat hypothalamus. They are involved in some physiological functions such as the control of feeding, energy metabolism and regulation of the sleep-wake cycle. SB-334867 can inhibit the orexin-A and orexin-B induced calcium responses in CHO-OX1 cells with pKB values of 7.27 and 7.23, respectively. SB-334867 is more selective for OX1 receptor over OX2 receptor. It causes 32.7% and 22% inhibition of orexin-A and orexin-B induced calcium responses in CHO-OX2 cells, respectively. Moreover, SB-334867 is found to reduce both orexin-A-induced and fasting-induced food intake. The acute anorectic effect of it is associated with signi®cant reductions in all active behaviours .