The effect of 7 commerically produced enzyme preparations on reducing the viscosity of rye grain substances in water extract (in vitro) and in the digestive tract of chicken (in vivo) was studied. The enzyme preparations tested were: FC-1 and FC-2 (amylase, protease, β-glucanase), DP-2885 and DP-2985 (amylase, protease, β-glucanase, cellulase), WF-078 (β-glucanase), Zymine xbp (xylanase, β-glucanase, pentosanase, cellulase, pectinase) and Avizyme (β-glucanase, cellulase, protease). Rye var. Dańkowskie Złote, containing 12.9% dietary fiber and 3.1% soluble fiber was used. The most efficient in reducing the viscosity of a water extract of rye flour (in vitro) and digesta (in vivo) was Zymine xbp (by 44 and 77% respectively), followed by DP-2885 (by 31 and 55% respectively), the effects of the remaining enzyme preparations were statistically insignificant. AME_N of unsupplemented rye was 10.97 ± 0.73 and supplemented with 0.1% Zymine xbp, 11.87 < 0.76 MJ per kg of dry matter. It seems that the usefulness of commercial enzyme preparations as additives to broiler diets based on rye may be preliminary checked by means of a simple in vitro test.