SUMMARYThe surface structures of 10 species ofPenicilliumconidia were studied and compared using the freeze-etching technique. The conidia of all species studied were shown to have an outer layer made up of“rodlets”which formed distinctive patterns. The patterns formed by these“rodlets”were species specific and therefore may have some taxonomic value. Variation was also noted between spores within species and the possible influence of heterokaryosis or the parasexual cycle or both on this variation in“rodlet”pattern is discussed.