Summary — Kinetics of growth of fungi associated with lps sexdentatus and Tomicus piniperda (Coleoptera: Scolytidae) and of the defence reaction of the inoculated scots pines. At 3 different seasons in the year, 5 species of fungi associated with I sexdentatus and T piniperda were inoculated into scots pine trees. Logs were also inoculated once during the year in the lab. The reactions were estimated by their length and by the quantity of resin (both total and concentration). The percentage of sieve cells filled with resin was appreciated by histological sections made in each reaction, at 10 and 30 mm from the point of inoculation and in the middle between this point and the end of the reaction. The kinetics of growth of the fungi and of the defence reactions (length, resin, histology) were followed for 60 days. The temperature and defence reactions were not sufficient to explain the differences in the kinetics of growth between fungi and between seasons (figs 1 and 7). Factors related to intrinsic characteristics of the fungi and to physiological state of the tree may play a role. The possible role of each fungus is discussed according to the induction of the reaction and to tree death when attacked by bark beetle populations. The wound periderm does not seem to be directly responsible for stopping the fungal growth. In return, the considerable slowing down of this growth, followed by a slowing down of the development of the reaction length (fig 3) may give sufficient time for the wound periderm to be built, to insulate the wounded tissues completely and to contain the aggressors. The parallel between the kinetics of growth of the fungi and the kinetics of resin accumulation suggests that the quantity of resin would depend upon the quantity of elicitor produced during the fungal growth. The reaction length in the phloem would depend on the diffusion ability of the elicitor. The end of the resin accumulation at a given place would not depend upon tissue saturation, but rather on the end of the elicitation at this place (compare figs 3, 5 and table III). After the end of the reaction growth, an homogenization process of the resin distribution may take place inside the reaction, by a diffusion of the resin from the highly concentrated zones to the less concentrated zones and, in some cases, by a continuation of the resin synthesis. A definition of 3 parameters representative for the defence reaction is proposed: speed, intensity, efficiency.