To optimize the efficiency of agricultural biogas units, 54 samples of pig slurry and manure were collected, and their methane potential (MP) was evaluated. They were characterized by the type of floor in the piggery, the physiological stage of animals, the management and the freshness of slurry and manure. The MP of the slurry of gestating sows, fattening pigs and piglets was 4, 13 and 28 Nm 3 CH 4 /t raw material, respectively. Many factors can explain this large difference, but the main one could be the water content, which also greatly affected the MP of slurry. The MP was 67 ± 3, 52 ± 13 et 41 ± 8 Nm 3 CH 4 /t raw material for accumulated solid manure of piglets, fattening pigs and gestating sows, respectively, but less differences were observed when expressed on an organic-matter basis (245, 197 and 230 Nm 3 CH 4 /t OM respectively). The MP of the faeces of fattening pigs was twice as high as that of the solid fraction of decanted-centrifuged slurry (71 ± 10 vs 37 ± 0.2 Nm 3 CH 4 /t raw material, respectively). The MP of slurry decreased as its duration of storage increased, for example, by 57% when stored for 4-5 months (MP expressed on an organic-matter basis). The MP of manure also decreased as its duration of storage increased, for example, by 16-41% depending on its type when stored for 2-3 months.