Aims of the research were to devise a proteome map of the chicken Pectoralis superficialis muscle, as resolved by two-dimensional gel electrophoresis, and to characterize protein expression changes in the soluble protein fraction in commercial conditions due to age and to time in transit before slaughtering. Broilers were reared under commercial conditions until they reached a mean 1.8 kg and 36 d, or 2.6 kg and 46 d of age. Transport to the slaughterhouse took 90 or 220 minutes. Transport-induced stress was assessed from blood metabolites and leukocyte cell counts, revealing significant changes in albumin, glucose and triglyceride concentrations, in heterophils and leukocyte counts for chickens in transit for longer, and in glucose depending mainly on age. The sarcoplasmic protein fractions were extracted from a total of 39 breast muscle samples, collected 15 min post mortem, for analysis by two-dimensional electrophoresis.