Spruce bud rust (caused by Chrysomyxa woroninii ) attacked both the leaf (needle) buds and ovulate strobili of Picea glauca and P. mariana. The infected needle buds produced extremely stunted shoots with bright yellow-colored needles. Infected cones became most conspicuos when aeciosori began to sporulate. Spermogonia were found exclusively at the apical region of infected needles, and also on the rims of scales on the dorsal side of infected cones. The nucleus was the most prominent feature of the small spermatia. Aeciosori, emerging from the stomatal bands, covered the entire length of the needle except for the apex region. On the cone, blisterlike aeciosori were produced on the dorsal and ventral sides of scales. Aeciosori were covered with a single layer of white, thick-walled, peridial cells. No viable seeds were produced by diseased cones. Aeciospores varied greatly in size and shape and were covered entirely with annular ornamentation. Most aeciospores that germinated produced a simple germ tube, but multiple germ tubes were also common. Germ tubes were non-septate and unbranched, and either anucleate, uninucleate, or multinucleate. There was evidence of secondary cycle infection caused by aeciospores.