Recently, a patented enzyme product (beta-Mannanase, Hemicell) has been shown to improve feed conversion in corn-soybean diets fed to broilers and swine. The mechanism of beta-Mannanase is to degrade beta-mannan, which is an antinutritional factor existing in many legumes, including soybean and canola meals. The objective of this study was to determine whether or not performance can be improved by including beta-Mannanase in diets of commercial laying hens, 18 through 66 wk of age. A 2 x 2 x 2 factorial arrangement of treatments was employed. There were two energy sequences of 2,926-2,907-2,885 and 2,827-2,808-2,786 kcal ME/kg, which changed at 33 and 43 wk of age respectively; two dietary enzyme levels (0 and 110 units/g); and two Hy-Line strains (W36 and W77). Hen-day production, hen-housed production, BW, feed intake, mortality, egg weight, and specific gravity data were collected biweekly. Data were analyzed in four cycles (each with six 2-wk periods) and also for the whole experiment. beta-Mannanase increased egg weight from 51.4 to 51.7 g/egg (P < 0.05) in the first 12-wk cycle. This effect was consistent across energy levels. beta-Mannanase significantly improved hen-day and hen-housed production after the first cycle. Hen-day production of the beta-Mannanase group was 0.70, 1.07, and 1.5% greater than the control for cycles two, three, and four, respectively (P < 0.01). After 30 wk of age, average hen-day production of hens fed the low-energy diets with beta-Mannanase was similar or superior to that of hens fed the high-energy diets without the enzyme. The study indicates that beta-Mannanase is capable of increasing egg weight in commercial layers at early stages of production, and increasing egg production, particularly delaying the postpeak decline in productivity.