The research objective was the definition of in-fluence of the peripheral speed, the direction of giving and the peripheral speed of rotation of chains for specific work. The results of pilot studies of spruce timber debarking by flail bodies are given in the study. The debarking by flail bodies is a way of mechanical impact on bark of forest product moving in the axial direction through the system of horizontal and vertical rotating shafts driving, on which the pieces of chains are attached. Due to centrifugal force the chains gain particular rigidity, and, influencing bark, force it down from the sur-face. Specific work of debarking was paid off as the work of duration of process (sec.) on the difference of indications of the working and single courses (W) referred to the volume of the removed bark (CBM), J/m3. Empirical and theoretical (normal) integral functions of distribution of deviation of specific work from mean values were presented. The matrix method of least squares of received regression models of the second order adequate to the exper-iment and lines of equal level of dependence of specific work on the peripheral speed of rotation of chain, speeds and the directions of giving were built. The standard errors of model was equal to 0.13 MDzh/m3 at passing giving and 0.18 MDzh/m3 were at counter giving. The coefficient of determi-nation of R2 models = 0.994 - at passing giving and 0.993 - at counter giving. In the study the lines of equal level of specific work depending on the pe-ripheral speed of rotation, speed and the direction of giving were presented. The results of research allow solving applied problems of the choice of pa-rameters and duties when developing the debark-ing machines by flail bodies.