The avian egg has a natural protective system composed of immunoglobulins and antimicrobial proteins/peptides. Its composition in immunoglobulins is known to vary depending on the immune status of hens; however, to date, no such evidence has been reported regarding antimicrobial egg molecules. To explore this hypothesis, laying hens were immune-challenged with three i.v injections of Salmonella Enteritidis lipopolysaccharide (LPS) at 24 hours intervals. Oviductal expression of 10 genes coding for egg antimicrobial compounds was analyzed by quantitative polymerase chain reaction. Antimicrobial activity of egg whites was assessed by turbidimetry against 8 bacterial strains. Our results showed that expression of four of the analyzed genes was significantly modified in response to LPS at 6 hours post-injection. At day 8, no differential gene expression was observed for most of genes. The global antimicrobial activities of egg whites towards Staphylococcus aureus, Salmonella Enteritidis, Salmonella Pullorum and Escherichia coli were significantly increased in eggs from LPS treated hens as compared to control animals. Our results suggest that the hen may enhance the albumen antimicrobial activity of its eggs when exposed to immune stimulations or infections. The quantification of the albumen antimicrobial compounds currently in progress will provide new informations about the underlying mechanisms.