A combine harvester (10) comprises a transverse threshing unit (26) arranged to receive and thresh a crop stream. Separating apparatus (32,36) are located downstream and rearward of the threshing unit and arranged to receive the threshed crop stream and convey in a rearward direction. Both the threshing unit and separating apparatus comprise respective grates (34, 42) for allowing grain and chaff to fall under gravity onto an underlying thresher pan (28) and separator pan (44) respectively. The thresher pan is driven in an oscillating manner to convey a primary grain/chaff stream rearwardly to a rear edge (49) from where the primary grain/chaff stream fails under gravity into a cleaning unit (48). The separator pan is also driven in an oscillating manner to convey a secondary grain/chaff stream forwardly to a front edge from where the secondary grain/chaff stream falls under gravity to combine with the primary grain/chaff stream. The cleaning unit comprising a fan (52) for generating a cleaning airstream (X,Y) which is directed through the falling grain/chaff stream. The separator pan front edge is disposed forwardly of the thresher pan rear edge by an overlap distance such that the secondary grain/chaff stream falls onto the thresher pan and stratifies before falling off the rear edge thereof.