The absolute and relative instantaneous growth rates of F1 hybrid chickens were determined  at 2- 10 and 12-20 week periods of growth. The hybrids were hatched from eggs laid by 69 Isa Brown and local chicken parents. A total of 123, 49 and 116 chicks of Isa Brown x frizzle feathered (IBxF), Isa Brown x naked neck (IBxNa) and Isa Brown x normal feathered IBxN) main crosses and 137, 42 and 64 chicks of frizzle feathered x Isa Brown (FxIB), naked neck x Isa Brown (Na x IB) and normal feathered x Isa Brown (NxIB) reciprocal crosses, respectively were produced at day-old. The greatest absolute growth rates of 49.44g/week at 2-10 weeks and 71.11 g/week at 12-20 weeks were obtained from IBxN and FxIB genotypes, respectively. Instantaneously, IBxNa had the greatest rate of 0.28 g/time at 2-10 weeks, while IB x F and Na x IB each at 12-20 weeks were found to grow at the greatest rate of 0.091 g/time, respectively. It was concluded that normal and naked neck genes could be utilised in main crosses to develop fast growing broiler chicks while frizzle and naked neck genes could be used in reciprocal crosses to improve good laying pullets without precocious maturity.