Karakul fat-tailed lambs were used to study growth and fattening effect of the α 2 -adrenergic agonist clonidine. Body weight, feed intake and fat tail size (volume, length and circumference) were measured weekly in ram lambs beginning at 9 wk of age when lambs were treated with saline (n = 4) or clonidine (n = 5, 20 μmg/kg/min) for three consecutive 28-d periods. Saline and clonidine were administered using 28-d Alzet osmotic pumps surgically implanted under the shoulder skin. Body weight gain (BWG) and tail volume gain (TVG) were elevated (P < 0.05) in period 2 relative to periods 1 or 3. However, the TVG/BWG ratio increased (P < 0.05) in period 2 and remained elevated in period 3. Thus, the TVG measurement reflected the increased tendency to fatten with advancing age. Clonidine had no effect on BWG or TVG. Tail circumference gain (TCG) and TCG/BWG tended (P < 0.16) to be depressed by clonidine in period 1 (P < 0.16) which suggests that a tolerance to clonidine may have developed.