and post-treatment in responders showed a significant difference (p<0.001), while nonresponders displayed no difference (p=0.86).A receiver operator characteristics (ROC) test was performed on those with two consecutive tests and the AUC was 0.72±0.5.At a cutoff of 22.5 ppm the sensitivity was 72% and specificity 62%.Evaluation of AUC showed controls to have 824±672 ppm*min, while responders 1127±795 were different from responders follow-up 532±647 (p<0.001),non-responders 916±878 were unchanged compared to follow-up 1133±1128.The ROC test of the AUC showed equal results as the peak values; 0.72±0.5.At a cut-off of 1000 ppm*min the sensitivity was 70% and specificity 64%.IBS patients responding to antibiotics displayed higher peak values (32±16) compared to healthy controls (p<0.001),while those not responding to treatment were similar to controls.Conclusion: Using appropriate cut-off levels, HBT can be used for determining bacterial overgrowth providing basis for treatment.A subgroup of IBS patients are identified with bacterial overgrowth thus responding to treatment.