The ultrastructure of representative types of ectomycorrhizal root of pine was analysed after collection at different times of year from March to June, using scanning and transmission electron microscopy. In the Pre-Hartig net zone (PHZ) near the root apex, a well-developed sheath is present in which are incorporated sloughed root cap cells. There is evidence of dissolution of the host cell wall adjacent to fungal elements in some cells. Sheath structure in the Hartig net zone (HZ) is similar to that in the PHZ, but the residual cells here are collapsed root hairs. Glycogen and polyphosphate granules are abundant in the sheath in March but their number declines in later months. The Hartig net is made up of a pseudoparenchyma of infolded fungal elements and the cortical cells adjacent to it are generally living. No basic difference between niycorrhizal and non-mycorrhizal cortical cells was observed, thus indicating that, in contrast to pathogenic attack, no adverse reaction to the fungal presence occurs. Reasons for seasonal changes of storage compounds are discussed.