A trial has been carried out at the experimental site at Grabów, which is situated in the Ma-zovian Plain in the Central Polish Lowlands, in order to calibrate the soil /crop water balance model ACCESS-II. The main interest of this site is that it furnishes data for 12 consecutive harvests of winter wheat Firstly, the principles of the model are described. Then the use of the model when the initial water contents are unknown. The first calibration results show that modifications need to be made to allow for the influence of severe winter frosts on crop growth. Following this modification, modelled yields were predicted to within 10 to 15% of measured yields, sufficient to demonstrate the strong link between yield, winter frosts and the amount of snow-cover protection. The discrepancies between measured and predicted values are useful in understanding the reasons for abnormally small yields. At this scale of modelling, the predictions are good enough to classify a region as very good, good or poor for winter wheat production under 'continental' climate conditions.