Two experiments were carried out to ascertain the possibilities of reducing the use of fodder phosphates in maize-soyabean meal and maize-rapeseed meal based diets for broiler chickens with the aid of phytase. In experiment 1, performed on 560 broilers (equal numbers of males and females), the effect of phytase on growth rate, feed consumption and feed conversion ratio was evaluated. The use of phytase resulted in improvement of feed consumption and body weight gains of chickens, but had no effect on feed conversion ratio. Phytase supplementation improved dressing percentage, especially in maize-rapeseed groups. In the balance experiment, performed on 80 chicks, Ca and P availability was determined. The use of phytase increased phosphorus availability by 24% in the case of soyabean diets, and by up to 29% in the case of rapeseed meal diets. The use of phytase allows production of broiler chickens using diets in which the total phosphorus level can be reduced by 33%.