During acidotic periods in a girl with a short small bowel, very high D-lactic acid concentrations were measured in blood and urine; the patient’ s characteristic faecal flora contained mainly lactobacilli, and during antibiotic cocktail treatment also many yeasts. In this case report we sought to understand the beneficial effect of the antibiotic cocktail. Microbiological analysis was performed in faecal samples. Total lactic acid in serum and urine was stud-ied using capillary gas chromatoygraphy-mass spectrometry, and D-and L-lactic acid in serum and urine by enzymatic assay. The results were coupled to patient’ s condition. Antibiotic cocktail therapy reduced the acidosis-associated symptoms, faecal lactobacilli and D-lactic acid production, but simultaneously the antiobiotic therapy strongly increased the percentage of yeast in the faecal flora. Four to six weeks after each course of treatment the percentage of yeast decreased, whereas the percentage of intestinal lactobacilli increased; D-lactic acid also simultaneously increased in blood and urine. The patient felt well and showed a high percentage of intestinal yeast, but she often suffered from acidosis owing to a high percentage of lactobacilli. The yeast was identified as the pathogenic Candida glabrata. From the mentioned data together with data from the literature it was concluded that during several weeks the selected pathogenic yeast, C. glabrata, acted as a microbiological and metabolic buffer. Shortly after he course of antibiotic treatment this intestinal yeast strongly competed with the intestinal lactobacilli and thus prevented renewed rapid growth, massive D-lactic acid production from glucose and consequently also D-lactic acid-associated acidosis. The emergence of this yeast led us to consider probiotic lactobacilli or yeast for therapeutic use. The lack of knowledge regarding bile acid-deconjugating activity in both lactobacilli and probiotic yeast means that a final recommendation is not yet possible. During acidotic periods in a girl with a short small bowel, very high D-lactic acid concentrations were measured in blood and urine; the patient ’s characteristic faecal flora contained mainly lactobacilli, and during antibiotic cocktail treatment also many yeasts. In this case report we sought to understand the beneficial effect of the antibiotic cocktail. Microbiological analysis was performed in faecal samples. Total lactic acid in serum and urine was stud-ied using capillary gas chromatoygraphy-mass spectrometry, and D-and L-lactic acid in serum and urine by enzymatic assay. The results were coupled to patient ’s condition. Antibiotic cocktail therapy reduced the acidosis-associated symptoms, faecal lactobacilli and D-lactic acid production, but simultaneously the antiobiotic therapy strongly increased the percentage of yeast in the faecal flora. Four to six weeks after each course of treatment the percentage of yeast decreased, while the percentage of intestinal lactobacilli inc reased; D-lactic acid also simultaneously increased in blood and urine. The patient felt well and showed a high percentage of intestinal yeast, but she often suffered from acidosis due to a high percentage of lactobacilli. The Yeast was identified as the pathogenic Candida glabrata From the mentioned data together with data from the literature it was concluded that several weeks the selected pathogenic yeast, C. glabrata, acted as a microbiological and metabolic buffer. Shortly after he course of antibiotic treatment this intestinal yeast strongly competed with the intestinal The emergence of this yeast led us to consider probiotic lactobacilli or yeast for therapeutic use. The lack of knowledge regarding bile acid-deconjugating activity in both lactobacilli and probiotic yeast means that a final recommendation is not yetpossible