The development of faecal bacteria composition in calves fed milk or a combined diet was investigated. On day 7, bifidobacteria in faeces of milk-fed calves already increased and did not change until the end of the study, whereas in calves fed the combined diet bifidobacteria only moderately increased and then decreased slowly until day 21. The counts of bifidobacteria in calves on a combined diet were significantly lower compared to those in milk-fed calves. The results showed that the occurrence of bifidobacteria in calf faeces is highly dependent on the diet composition. Faecal bacteria flora of calves fed exclusively by milk is rich in bifidobacteria, but in calves on a combined diet coliforms dominated.