This study was designed to determine the effect of prenatal temperature conditioning on hatching and live performance of laying chickens, and response to heat and cold stress during laying period. A total of 3600 eggs obtained from ATAK-S brown parent stock were incubated at control (37.5 degrees C, CONT-Inc), cyclic low (36.5 degrees C/6 h/d from 10 to 18 d of incubation, LOW-Inc) or high (38.5 degrees C/6 h/d from 10-18 d of incubation, HIGH-Inc) incubation temperatures. Hatched chicks per incubation temperature were reared under standard rearing conditions up to 26 wk. From 27 to 30 wk, hens from each incubation temperature were divided into 3 environmentally controlled rooms and reared at control (20 +/- 2 degrees C, CONT-Room), low (12 +/- 2 degrees C, COLDS) or high (32 +/- 2 degrees C, HEATS) temperatures. Hatching performance, body weight, egg production, and plasma triiodothyronine (T-3) and thyroxine (T-4) levels and oxidant and antioxidant activities were evaluated.