AIM: To investigate the effect of a four-week consumption of a special Hungarian probiotic agent (Biofir(R)) on the faecal microflora in human healthy subjects.METHODS: The effect of Biofir(R) with 106/cm3 initial germs on the faecal microflora was studied in 120healthy volunteers (71 females, 49 males). The traditional Russian type kefir was used as control. The various germ groups and pH values were determined in wk 2, 4and 6.RESULTS: The number of all microbes increased during the 4-week probiotic treatment. The number of microbes increased 4.3-fold in the control group and 6.8-fold in Biofir-treated group. The probiotic kefir caused multiplication of the probiotic flora, meanwhile the undesired bacteria multiplied in the control group. No significant change of pH values of the faeces was found in both groups.CONCLUSION: The Hungarian probiotic kefir (Biofir(R)) is capable of promoting multiplication of probiotic bacterial flora in the large bowel.