The apoptosis-associated speck-like protein with a caspase-recruitment domain (ASC) adaptor protein bridges inflammasome sensors and caspase-1. Upon inflammasome activation, ASC nucleates in a prion-like manner into a large and single platform responsible for the recruitment and the activation of caspase-1. Active caspase-1 will in turn promote the proteolytic maturation of the pro-inflammatory cytokine IL-1β. ASC oligomerization is a direct evidence for inflammasome activation and its detection allows a read-out independent of caspase-1 and IL-1β. This protocol describes how to detect the oligomerization of ASC by Western blot.