Ingested fungal enzymes are responsible for cellulose digestion in the xylophagous larvae of four species of cerambycid beetles from four different subfamilies: Bellamira scalaris (Lepturinae), Graphisurus fasciatus (Lamiinae), Orthosoma brunneum (Prioninae) and Parandra brunnea (Parandrinae). When the larvae are maintained on their normal diets of fungus-infected wood, their midgut fluids are active against microcrystalline cellulose, and they are able to digest 14C-cellulose. By contrast, when larvae are maintained on fungus-free, enzyme-free diets, their midgut fluids lack cellulolytic activity, and they are unable to digest labeled cellulose. We argue that ingested fungal enzymes may be responsible for cellulose digestion in many, perhaps even all, xylophagous larvae from the three coleopteran families Anobiidae, Buprestidae, and Cerambycidae.