The effectiveness of different commercial bacterial preparations such as Lactostatic AC and Probios and own preparations, Bb and Sf containing Bifidobacterium bifidum (poly-strains) or Streptococcus faecium, on calf performance were investigated in an experiment on 50 calves divided into 5 groups of 10. Probios and Bb used as additives to the diet for calves increased their daily body weight gain by an average of 9 and 10% over the control group (P < 0.05), Lactostatic AC and Sf improved daily gains by 3 and 6%, respectively. A higher growth rate was related to a higher (8%) intake of concentrate mixture. A tendency towards higher feed efficiency was observed in calves with higher growth rate.