Objective: To describe the results of laboratory tests performed on biological samples from patients with Guillain-Barré syndrome (GBS) submitted to the Instituto Nacional de Salud (INS) between 2018 and 2019. Materials and methods: We conducted an observational study on patients with GBS, by using data from the epidemiological surveillance system. Biological samples, previously analyzed at the INS, were obtained to study arboviruses, respiratory viruses, enteroviruses and enterobacteria, among others. Results: A total of 2,051 specimens were obtained from 906 patients with GBS. Three patients tested positive for dengue and three for Zika. In 19 patients, the stool culture was positive for Campylobacter jejuni. Phylogenetic analysis of 10 Campylobacter jejuni strains classified them as genotype ST2993, which was previously reported in China and associated to a GBS outbreak. Twelve cerebrospinal fluid samples tested positive for enterovirus by PCR in 2018, but none could be verified by culture or complete genome sequencing during the study. One patient was positive for influenza A, two for influenza B, two for adenovirus, five for respiratory syncytial virus, and ten for rhinovirus. Conclusion: Several pathogens were found in samples from patients with GBS. However, we found that the genotype ST2993 of Campylobacter jejuni was the most likely causal agent, a pathogen that is related to GBS outbreaks in different continents. It is necessary to confirm this hypothesis with additional analytical studies and it is important to describe the transmission mechanism of C. jejuni genotype ST2993 in order to implement prevention and control measures.