BACKGROUND : This work aims to determine how antibiotic therapy influences MR spectroscopic findings in patients undergoing treatment for pyogenic brain abscess. METHODS : This prospective, single center study included all patients who received treatment for brain abscesses at the Neurosurgery Department of University Hospital Ostrava between 2012-2017. Pre-operative MR imaging was carried out on all patients including diffusion-weighted imaging and in vivo single-voxel proton spectroscopy with intermediate echo time. The following factors were evaluated: duration of antibiotic therapy, characteristics of MR imaging and spectra findings and culture results. RESULTS : MR spectroscopy findings characteristic of brain abscesses, i.e. the resonances of at least one of the metabolites concerned (amino acids, acetate, alanine and succinate), were observed in 23 patients who had undergone antibiotic therapy for less than 72 hours beforehand (median 7 hours; IQR 30 hours). The 20 patients who underwent antibiotic therapy for longer than this (the median time was 336 hours with an IQR of 284 hours) showed no abscess-specific metabolites, only nonspecific lactate and/or lipid resonance (p <0.0005). These results were further compared with culture findings of pus samples taken intra-operatively: a significantly higher rate of positive culture (78,2%) was determined in cases where antibiotics were administered less than 72 hours before MRS (p <0.0005). CONCLUSIONS : Prolonged antibiotic therapy can influence MRS findings in pyogenic brain abscesses - a fact which is certainly necessary to take into account in its differential diagnosis. The disappearance of the characteristic metabolites can be indirectly interpreted as an indicator of successful antibiotic therapy in cases where surgical intervention is not possible. Further study in this field is required to confirm the results of this study.