Healthy Norway spruce trees were investigated over 130 weeks following successful attack by the bark beetle Ips typographus in a study of fungal invasion. The study was undertaken in southeastern Norway during an epidemic period. Sapwood moisture was measured and the tree reaction and beetle activity were noted, fungal invasion was examined in disc samples taken 1, 5, 10 and 15 m above stump height. The fungal penetration in the sapwood started very slowly, but accelerated during the fourth week after attack. The leading edge of fungal penetration was a few millimeters in advance of the visible blue-stain until the heartwood was reached. The development of blue-stain was similar in Lardal, 1979, and at Ås, 1980, but with some differences related to the air temperature. Fungi were found to invade the sapwood successively. The pathogenic species, Ophiostoma polonicum, was the primary invader occurring during the first week, followed by other beetletransmitted species. The secondary invaders, O. bicolor, Graphium sp. 1, O. penicillatum and O. ainoae, entered the sapwood during the first three weeks after attack and reached a peak within ten weeks. The tertiary invaders, probably also beetle transmitted, were not as common as the secondary colonizers. The first Hymenomycetes, rather weak white-rotters, appeared among the tertiary invaders. Later succession was dependent on the moisture content of sapwood. Strong decaying whiterotters entered the sapwood near the base where the moisture content remained favourable, while cf. Trichoderma viride dominated in the drier parts of the trees, where the sapwood moisture declined to fibre saturation point 75 weeks after attack. The heavy beetle attack, averaged 3.7 entrance holes per dm² over more than ten meters of the stem, overwhelmed the trees rapidly and no secondary resinosis occurred. [ABSTRACT FROM AUTHOR]