In this study, two upflow anaerobic sludge blanket (UASB) reactors seeded with aerobic activated sludge were used to treat brewery wastewater. The reactors were identical in design and were continuously operated at 19-24 degrees C. Reactor A war seeded with 1.98 g volatile suspended solids (VSS) per liter of acclimatized activated sludge, while Reactor B was seeded with 1.98 g VSS l(-1) of acclimatized sludge and 3.95 g VSS l(-1) of unacclimatized sludge (a total of 5.93 g VSS l(-1)). The study examined reactor performance in terms of treatment efficiency and methane production under different hydraulic retention times (HRT) and organic loading rates, and evaluated the effect of amount of seed sludge on reactor start-up and performance. The results indicate that as the chemical oxygen demand (COD) loading rate increases with time, the influence of the amount of seed sludge becomes more pronounced. Reactor B consistently out-performed Reactor A under shorter HRTs of 1.5 days to 12 h with maximum COD and VSS removal rates of 91% and 81%, respectively at a sludge lending rare of 0.25 g COD g(-1) VSS day(-1) anti an HRT of 18 h. The results also confirm that an acclimation period of at least 2 weeks is necessary to prevent delays in the start-up process when using activated sludge as seed. Using 5.93 g VSS l(-1) of activated sludge as seed enabled Reactor B to achieve satisfactory, performance.