This study assesses, from the economic perspective, cost-effectiveness of substitution of variable factors, i.e. mineral fertilisers (SE295), with plant protection products (SE300) in the process of crop production of commercial farms in Poland. The analysis was based on the Cobb-Douglas production function model, which was to analyse substitution of the factors. In 2010, the surveyed sample covered 8,583 and in 2011 – 8,378 commercial farms. From the economic perspective, substitution of mineral fertilisation with plant protection products was beneficial for improvement of crop production efficiency of commercial farms. In 2010, this resulted from three times higher (3.01) rate of transformation of the plant protection product factor into plant bioproduct. In 2011, the ratio amounted to 2.65 to the advantage of plant protection products. The higher the difference between the rates, the higher the economic efficiency of substitution between substitutes.