Two experiments were carried out to analyze the effect of Elfazepam, a minor tranquilizer, on the eating and ruminating behaviour of sheep fed Sudan grass (Sorghum sudanese STAPF.) hay or pelleted concentrate (barley and wheat bran) (ad libitum) (Expt. I), and Alfalfa (Medicago sativa L.) hay (2% BW /day) (Expt. II). In Experiment I, 0, 0.05 and 0.10mg/kg BW of Elfazepam dissolved in ethyl alcohol were administered orally to 3 non-pregnant ewes twice a day during 7 days (roughage diet) along with 0.1mg/kg BW of Elfazepam (concentrate diet). In Experiment II, Elfazepam at the same level as in Experiment I was orally administered to 3 wethers for 2 weeks in a 3 X 3 latin square design. Elfazepam administration resulted in the increase of feed intake which lasted for 7 days when sheep were fed a concentrate diet, though the response to Elfazepam disappeared 5 days after the initiation of the administration in sheep fed the roughage diet alone (Expt. I ). In sheep with restricted feed, Elfazepam increased the rate of eating and decreased the chromium (Cr) passage rate through the gut, although there were no differences in the rumination parameters (Expt. II). On the basis of these results, it is suggested that the action of Elfazepam on feed intake decreases when the ruminal retention time of ingesta is the factor limiting feed intake due to its suppressive effect on the passage through the digestive tract.