1. A total of 420 male 1-d-old chicks of a slow-growing genetic line (Hubbard ISA Red JA) were used as the trial material. Two diets that were low in fats and high in cereals, and free from growth promoters and animal protein, and formulated at two energy and protein concentrations, were fed ad libitum or 80% of ad libitum. The birds had access to pasture from 14 d to slaughter at 84 d of age. 2. The treatment groups were: Dilute-AL (energy and protein diluted diet fed ad libitum), Dilute-R (restricted energy and protein diluted diet), High-AL (high energy and protein diet fed ad libitum), High-R (restricted high energy and protein diet). 3. Daily weight gains and feed consumptions were recorded in each replicate. 4. The live weight on d 84 was lowest in the Dilute-R group, whereas the highest live weight was in the High-AL group. The highest feed consumption was found in the Dilute-AL and High-AL groups. The worst feed conversion ratio was determined in the Dilute-AL and Dilute-R groups. The effect of treatments on mortality was not significant. 5. The best feed conversion efficiency was obtained in the feed-restricted group receiving the high energy and protein diet. The results suggest that forage may contribute to the nutrition of slow-growing free range broiler chickens if suitable pasture species are grown.