The objective of the presented work has been the determination of the longitudinal shrinkage of the beech wood (Fagus sylvatica L.) containing different proportions of the fibrous reaction G-cells. The results of the measurements (Table 1) can be summarized in the following points: 1. A heavily developed reaction wood has the average longitudinal shrinkage value 0, 79per thousand. 2. A slightly developed reaction wood shrinks in the longitudinal direction 0, 39per thousand. 3. The wood from the opposite of the developed reaction wood shrinks in the longitudinal direction only 0, 13per thousand. 4. A normally developed beech wood without the fibrous reaction G-cells shrinks longitudinally only 0,12per thousand. 5. The longitudinal shrinkage of the beech wood is proportional to the content of the fibrous reaction G-cells.