SB-399885 hydrochloride 10 mg/kg significantly increases wakefulness (W) (F(3,15)=3.32, P<0.05) while slow wave sleep (SWS), rapid-eye-movement sleep (REMS) and the number of REM periods are reduced (F(3,15)=4.0, P<0.01; F(3,15)=3.14, P<0.05 and F(3,15)=2.62, P<0.05, respectively) Compare with the control vehicle . Analysis of sleep variables in 2-h blocks shows that SB-399885 hydrochloride 10 mg/kg increases W (F(3,15)=5.48, P<0.01) and reduces SWS (F(3,15)=5.42, P<0.01) and REMS (F(3,15)= 4.05, P<0.01) during the first 2-h period. SB-399885 hydrochloride 5 and 10 mg/kg augment light sleep over the first (F(3,15)=3.46,P<0.01 and F(3,15)= 3.65, P<0.01, respectively) and the second (F(3,15)=3.23, P<0.05 and F(3,15)=3.08, P<0.05, respectively) 2-h recording periods. SB-399885 hydrochloride 10 mg/kg significantly increases REMS latency (F(3,15)=3.60, P<0.01) and reduces the number of REM periods during the first 2-h of recording (F(3,15)=3.88, P<0.01).