On the adoption of a sampling method for the estimation of the yield of small experimental plots, the need arose for a threshing machine capable of threshing quickly and accurately the small sampling-units which comprise the sample from an individual plot. These sampling-units contain various numbers of ears from some three or four to twenty or more, and there is no commercial machine which deals adequately with such small quantities of grain. The number of sampling-units from a typical randomised block experiment may amount to 2500, and to thresh and winnow such numbers in two distinct operations would take no inconsiderable time. As a direct result of this, a machine was constructed in which these two operations were successively performed, without the need of handling the intermediate products. It is the object of this paper to describe this machine and the manner in which it was used for this purpose at Rothamsted last season. Wheat, oats and barley were treated, only minor alterations of the size of the screens, the speed of rotation and the strength of the blast for the separation of the chaff being necessary.