Two hybrid upflow anaerobic sludge blanket (UASB) reactors were used to treat screened swine wastewaters. In order to achieve the advantages of both suspended growth and attached-growth anaerobic reactor systems, this type of reactor has a rope matrix inserted as a fixed-film medium in its mid section. The study examined the reactor performance in terms of its treatment efficiency and methane production, and evaluated the effect which the absence of seeding in the start-up process had on the efficiency of reactor performance. The conclusion reached was that this hybrid UASB reactor could be used without seeding in the treatment of screened swine manure if the organic loading rates were moderate. Under these conditions, over 57% COD removal and 0.71 litres CH4/litre reactor day were obtained. While sludge loss did occur, methane production increased and the concentrations of VFA in the effluents were kept below 100 mg/litre. It is believed that the additional biofilm in this hybrid reactor increased the stability of the reactor and helped maintain steady methane production. The results also confirm that granulation of the sludge is an essential requirement for satisfactory operation.