A total of 384 male broiler chickens were divided into four groups, 12 replicates each with 8 birds per replicate. Four barley-based diets were prepared. The control diet (C) was unsupplemented, diet A was supplemented with flavomycin (10 mg/kg), diet OS was supplemented with organic acids (3 g/kg) and a symbiotic composed of a probiotic and lactose (1:2, w/w), diet E was supplemented with β-glucanase (1 g/kg). Diets were fed from 1 to 35 days of age. In the OS group the body weight gain (BWG) was highest (P<0.05), while feed conversion ratio (FCR) was similar as in group E, but better (P<0.05) than in groups A and C. The viscosity of ileal digesta was 1.55 in group E, while in the remaining groups it averaged 2.37 mPas.s (P<0.05). The pH of caecal digesta was lowest in group OS (5.88), followed by E (6.06), while in groups A and C groups it averaged 6.33 (P<0.05), which points to increased production of short-chain fatty acids. It seems that a combination of organic acids and a symbiotic can replace antibiotic growth promoters in broiler diets.