The ! present work of investigation had like obj ective to evaluate the effect of an Imrnunomodulating antiestresante in the stages of pre-beginning, beginning and 1 growth ofmeat chickens ofthe line Cobb 500. The evaluated parameters were: gain 1 of )Veight, food consumption, nutritional conversion, mortality and index of productive efficiency (I. P. E). Eight hundred birds distributed at random in two treatments, experimental witness were used. To the experimental treatment him pro~ision in the drink water the immunomodulating antiestresante in the stage ofPre- 1 Beginning: 0.30ml, in the stage of Beginning: 0.35ml and in the stage of Growth: 1 0.3~m1 respectively. The used estadisctic design was Design ofBlocks Completeíy at Random. The major increases of alive weight were in MALE experimental treatments EXP (3107.60g) and EXP FEMALE (2504.70g) with respect to the tre~tments witnesse...