1. Various growth rates of chickens were induced with different nutritional regimes, and the collagen content and architecture of the medial part of the puboischiofemoralis muscle were compared among 21-d-old chicks and 80- or 95-d-old broilers. 2. The percentage muscle weight relative to live weight increased from chicks to 80-d-old broilers and the 95-d-old broilers attained the largest percentage. An inter-relationship of the percentage muscle weight and the growth rates of birds could not be determined. 3. Collagen concentration was related to the growth rates for the first 21 d post hatching and maintained the same level during the later stages up to 80 d. The 95-d-old broilers, that were subjected to early rapid growth followed by restricted later growth, had the highest collagen content. 4. On SEM (Scanning Electron Microscopy) photographs, endomysial honeycombs were small and encircled by perimysia of a collagen network with small mesh size. Thin and thick perimysia were distinguished and the expanded portion of thick perimysia was also observed. Generally, the perimysia were made up of rough collagen tissue where fatty tissue developed, especially in the broilers. 5. Perimysial collagen fibres with mainly transverse striation were divided into two fundamental types, wide collagen platelets and narrow cords. With growth from the chick to broiler stage, features of the collagen fibres did not change regardless of expansion of the thick perimysia. Endomysia increased slightly from thin to thick meshwork as growth progressed. However, the collagen architecture of the muscle in broilers did not change under different nutritional regimes. 6. In conclusion, the puboischiofemoralis muscle of chickens develops relative to live weight when later growth is limited in broilers, but the collagen architecture is not affected by the different growth rates.