The experimental designed to measure the effect of darkening programs on growth rates and some blood parameters in broiler chicks. Six hundred Ross308 chicks Wing-banded at 1-day old were divided into four trail groups, each with 3 replications. The chicks were raised on ground litter containing sawdust. Chick's were subjected to four darkness program: Treatment 1, serviced as a control (24 light + zero dark), Treatment 2 (18 L + 6 D continues when chicks arrived 150 g), Treatment 3 (1 hour of darkness at 2ndday, 2 hours of darkness at the start of the 2nd week, 3 hours of darkness at the...