Effects of 3 eggshell temperatures (EST; 36.7. 37.8, and 38.9 degrees C) in 2 genetic laying hen crossbreds (AB and BB; same hen line, different rooster line) on embryonic metabolism and hatchling quality were investigated. EST were applied from day 14.5 of incubation (E14.5) until hatching. The experiment consisted of 6 consecutive batches with eggs weighing between 59 and 61 g. Heat production was determined continuously from E14.5 onward. In fresh eggs, yolk weight tended to be higher (Delta = 0.28 g; P = 0.08) in the AB crossbred than in the BB crossbred. At E14.5 and E18.5, yolk-free body mass (YFBM) and residual yolk (RY) weight did not differ between genetic crossbred and EST. Hatching time after the start of incubation was not affected by genetic crossbred, but was longer in the 36.7 degrees C (517 h) than in the 38.9 degrees C (505 h), with 37.8 degrees C in between (506 h). At 6 h after hatching, no differences between crossbreds were found for chicken quality parameters, such as chicken weight, chicken length, RY, YFBM, and organ weights, but heart weight was higher in the 36.7 degrees C EST than in the other 2 EST (Delta = 0.24 to 0.30% of YFBM, P = 0.005). Intestinal weight was higher at 36.7 degrees C EST than at 38.9 degrees C EST (Delta = 0.79% of YFBM; P = 0.02), with 37.8 degrees C EST in between. Heat production between E14.5 and E18.5 was higher in the AB crossbred than in the BB crossbred (Delta = 2.61%, P < 0.001) and regardless of crossbred higher at an EST of 38.9 degrees C than at other 2 EST (Delta = 3.59% on average; P < 0.001). Hatchling quality determined at pulling (E21.5) was not affected by EST, but AB chickens were lighter (Delta = 0.46 g; P = 0.03), had less red hocks (Delta = 0.03; P = 0.02), more red beaks (Delta = 0.10; P < 0.001), and a higher (worse) navel score (Delta = 0.11; P < 0.001) than BB chickens. It can be concluded that not only incubation temperature, but also the rooster line appears to play a role in layer crossbred embryo metabolism and hatchling quality.