The effect of feeding calves of the Black-and-White East Friesian breed on milk replacers based on proteins of animal origin were investigated. Skim milk powder was substituted at the levels of 0, 25, 50, and 75% by protein from fish protein concentrates produced using enzymatic hydrolysis. The performance of calves, i.e. body weight and daily gain, was assessed and nutrient digestibility and nitrogen balance were estimated. There were no differences in daily liveweight gain during the whole period of the study (about 790-830 g) and in the liveweight of calves at the end of experiment (about 127-132 kg). Up to 60 days of age the daily gains of calves from control group (without fish protein) were higher (P<0.01), 709 g, than in remaining groups (689-621 g). The results show that up to 75% of milk protein in milk replacers may be successfully substituted by fish protein concentrate protein without adversely affecting calf performance.