During the last decade the invertebrate Galleria mellonella has successfully been used as a powerful and reliable model host for the analysis of bacterial pathogenesis as it offers an inexpensive and ethically acceptable alternative to the usage of eg rodents in infection research. 1 In this context, Galleria mellonella is of special importance for biomedical research with focus on innate immune activation in inflammation and infection. Recently, Galleria mellonella transcriptome analysis revealed the presence/identified proteins related to immune signaling which are homologuous to their vertebrate counterparts. 2 The presence of these highly conserved innate immune mediators makes G. mellonella a good model for the investigation of innate immune system activation by microbe associated molecular pattern (MAMP) which mediate the initial interaction of microbes with the host. Therefore, MAMPs play a key role in activation of the innate immune system in vertebrates as well as in invertebrates. One of the most frequently studied MAMPs in insect immunity is LPS being a main compound of the Gram negative bacterial cell wall. LPS is often used as an immune elicitor in virulence studies or in gene expression studies using Galleria mellonella. 2, 3 In addition, LPS is used as a standard positive control in many assays focusing on activation of the innate immune system, first to facilitate the interpretation of the data and, second, to ensure the technical validity. However, when using LPS, one must be aware that different bacterial species express different LPS with different bioactivity, 4 and second, that distinct commercially available LPS dramatically differs in purity. This is an important point since only LPS labeled as “ultrapure” is almost completely free from contaminants such as components of the gram negative cell wall other than LPS, finally inducing a specific and defined LPS-mediated immune response in experimental settings. However,“standard” or “crude” commercially available LPS contains other components of Gram negative bacteria, including ie peptidoglycans or lipopeptides, finally resulting in a mixed and non-standardized immune response due to an undefined stimulus. In many publications, unfortunately, the information on the LPS used is inaccurate or missing. Often, the origin species or the degree of purity of the LPS used are not indicated, a fact that unnecessarily decreases the reliability of published experiments. In our work, we provide evidence that these informations are absolutely essential as distinct commercially available LPS achieve significantly different results. We used “ultrapure”(UP LPS, tlrl-peklps) or “standard”(ST LPS, tlrl-eklps) Escherichia coli K12 LPS of the same manufacturer (Invivogen, Toulouse, France). Standard pure LPS is manufactured via phenol extraction and contains TLR2 and TLR4 activating compounds while ultrapure LPS is manufactured using additional enzymatic treatments and purified by the phenol-TEADOC extraction protocol. 5, 6 The purity was verified using human embryonic kidney cells overexpressing murine TLR2 or TLR4-MD2-CD14 receptor complex. UP LPS only activated TLR4-dependent signaling, while ST LPS activated both, TLR2-and TLR4-dependent signaling (data not shown). This clearly indicates that ST LPS contains additional co-components, like peptidoglycanes or lipopeptides, other than a defined TLR4 ligand. Therefore, this ST LPS is an inappropriate tool to investigate a defined TLR4-dependent signal. This finding is also of utmost relevance to