By entering the bloodstream, Gram-negative bacteria cause immune system reactions and lead to the activation of different chains of non-cellular reactions. One of the components of the cell wall of this family of bacteria are lipopolysaccharides, which form complexes of high molecular weight known as bacterial endotoxins, due to the toxic effect that they cause in other organisms. Almost any environment is appropriate for the development of Gram-negative bacteria, given that contamination with these bacteria is very common. There are several diseases related to the endotoxins of Gram-negative bacteria affecting humans. We will discuss six of them in this article.