Feeding 2‐weeks old broiler chicks on gibberellic acid (GA3)‐containing diets (0, 1, 5, 25 and 125 ppm) for 3‐weeks led, generally, to nonsignificant increase of body weight, decreased feed consumption and better feed conversion (on 25–125 ppm). Yet, the percentages of the carcass and the other organs (liver, gizzard, heart) and glands (adrenal, thyroid and pituitary) weights were lower comparing with the control (0 level). Blood protein and magnesium concentrations raised significantly. Blood glucose increased but not significantly. There was remarkable decrease (P≤.01) in transaminases activity. The muscular protein decreased, whereas the fat percentage significantly increased. The bone reflected lower density and mineral (calcium, magnesium and phosphorus) contents. GA3led to numerous histological lesions in different organs. Two‐weeks withdrawal period did not ameliorate the negative effects of GA3‐inclusion whether on the dressing percentages, blood picture, or on the muscles and bone constituents.