1. The object of this study is the optimization of the grain harvesting operations by minimizing the total harvest costs under weather conditions prevailing in the centre of the Netherlands. The sequential grain harvesting operations consist of: combining-loading of grain wagons-transport-unloading-ventilated storage-drying-dry storage.The capacities required of the sequential operations are mainly determined by the grain moisture content and therefore by the weather. This especially concerns the capacities of combining, drying and ventilated storage. As the weather is the key factor and varies from year to year, the criterion becomes the minimization of the average annual total harvest costs for a given cropping program over a large number of years. The total harvest costs comprise the field losses of the mature crop and the costs of personnel and harvesting equipment.Also the harvesting organization has been studied; a system was developed to provide minimum costs of the separate components: combining, transport, drying and storage with a view to the minimum costs of the system as a whole. Selecting a system with minimum costs can only be carried out with a view to the organization of a particular farm and taking into account the conditions prevailing on that farm. Therefore, the results found have been used to minimize the total harvest costs for a 20,000 ha grain farm under the actual weather occurring during the harvest periods of the years 1931-1967.2. The farm is a part of the reclamation enterprise of the Yssel Lake polders Development Authority which is responsible for the integral development of the polders in the Yssel Lake.Owing to the high moisture content of the mud, the land is not ready for the planned land use immediately after reclamation. Hence a period of at least five years of farming by the Authority is required to transform the mud into a good soil. The crops grown on this temporary farm are: colza, barley, oats, wheat, alfalfa and flax. The first four of these crops (14,000 ha) are ...