The aim of this study was to determine the effect of thermal manipulations during early embryogenesis (EE) and late embryogenesis (LE) on body temperature of Japanese quails (Coturnix coturnix japonica). Incubation conditions from day 0 to day 17 were 37.78 degrees C and 55% relative humidity for control group. In the thermally treated eggs during EE (EE6, EE7 and EE8 days), incubation temperature was increased to 418 degrees C and relative humidity to 65% for 3 hours (12:00-15:00) on the sixth, seventh and eighth days of incubation. Also, in the LE stage (EL12, EL13 and EL14 days), incubation temperature was increased to 418 degrees C and relative humidity to 65% for 3 hours (12:00-15:00) on the 12th, 13th and 14th days of incubation. Average temperature, relative humidity and total heat of indoor air were changed from 28.71 to 30.448 degrees C, from 45.69 to 57.15% and from 14.67 to 16.16 kcal kg(-1) dry air, respectively. Higher total heat of indoor air in 10-11 weeks than that of other weeks was found. Significant differences between the control (41.52 +/- 0.268 degrees C) and manipulation groups were found, but no significant difference between the EE (41.23 +/- 0.408 degrees C) and LE (41.26 +/- 0.378 degrees C) groups with respect to body temperatures. Body temperatures of quails were measured as 41.55 +/- 0.318 degrees C, 41.56 +/- 0.268 degrees C; 41.17 +/- 0.338 degrees C and 41.07 +/- 0.308 degrees C at 10, 11, 12 and 13 weeks of age, respectively. In addition, differences among the weeks in point of body temperatures of quails were found to be significant (p <0.01).