A field study of 38 dairy farms was set up to determine the relationships between feeding management, grassland management and feed costs/100 kg milk, 305-day milk yield and nitrogen surplus/ha. Data of the farms were on management (based on questionnaires), grassland calendar, milk yield and economic data for May 1996 to May 1997. Partial Least Squares (PLS) was used to analyse data, because of the large number of variables relative to the number of farms. The R2 of the models varied between 0.32 (nitrogen surplus model) and 0.60 (feed costs model). The nitrogen surplus model did not have predictive relevance. The PLS-model for feed costs resulted in the hypotheses that (1) a high percentage of pasture that cannot be grazed by the cows results in an increase in feed costs, (2) a high percentage of grazings lasting >4 days increases feed costs, (3) mistakes in set-up of the paddocks cannot be compensated for by exact planning, and (4) farmers who have not organized their grazing management well, also tend to have worse results as to their silage management. The milk yield model showed that a high milk yield/cow is realized on farms with too low a number of growing days for cutting.