Whey (pH 4, 6 and 8) was substituted for manure at 25, 50, 75 and 100% to study the effect of whey on anaerobic biogas production. The sample weights were adjusted to provide the same total chemical oxygen demand since on a weight basis whey has double the chemical oxygen demand of manure. The mixtures, along with an activated sludge and mineral and vitamin supplement, were placed in 140-mL glass bottles fitted with a syringe inserted through a rubber septum. The samples were incubated at 35°C, and when gas had filled the syringe (~60 mL) the syringe was withdrawn and gas composition measured using gas chromatography and volume of methane and hydrogen produced was calculated. Then the syringe was replaced and digestion and gas collection continued. Statistical analysis was performed with effects of percent whey (n = 4), whey pH (n = 3) and sampling time (n = 3) and their 2-way and 3-way interactions. Percent whey significantly (P ≤ 0.01) affected volume of hydrogen and methane produced as well as pH at the end of digestion. Biogas from mixtures containing 25% or 50% whey contained primarily methane and no or little hydrogen and were not significantly different from each other. Biogas from mixtures containing 75% or 100% whey contained primarily hydrogen and no or little hydrogen and were not significantly different from each other. The pH of the whey had less effect on gas production than whey percent. The difference in biogas composition was explained by the higher level of fermentable carbohydrate (lactose) in whey. After digestion, pH was significantly decreased when whey percent was increased to 75%. Mean pH values were 6.51, 6.50, 6.36, and 6.19 for mixtures containing 25, 50, 75, and 100% whey, respectively. Adding more than 25% whey caused more inconsistent gas production (i.e., greater variation in time to produce the first 60 mL of gas, and more failures occurring during digestion (i.e., gas production ceased before the end of the experiment). Having a highly fermentable sugar such as lactose as part of a waste stream, causes a drop in pH during anaerobic digestion and this needs to be considered when designing digester systems for use by artisan cheese makers.