Abstract.. Two species of Ceratocystis are described from western North America. Ceratocystis rufipenni Wingfield, Harrington, & Solheim is associated with the North American spruce bark beetle Dendroctonus rufipennis infesting both Engelmann spruce (Picea engelmannii Parry) and white spruce (Picea glauca (Moench) Voss) in British Columbia. This fungus is a primary component of the bark beetle mycota and has a relatively high degree of virulence to Engelmann spruce. Ceratocystis douglasii (Davidson) Wingfield + Harrington was previously described as Endoconidiophora coerulescens f. douglasii. It is common on Douglas-fir lumber in western North America where it causes blue stain. Both fungi grow optimally at low temperatures and produce perithecia only after extended incubation under refrigeration. Ceratocystis rufipenni produces conidiophores mostly in association with perithecia, whereas conidia and conidiophores of C. douglasii are produced abundantly on wood and agar.