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The cell wall structure of Salmonella typhimurium has been studied for the first time during transit from free‐living to parasitic lifestyles. Peptidoglycan of S. typhimurium proliferating within human epithelial cells contains a high proportion of previously unidentified muropeptides (5–10‐fold higher than in extracellular bacteria). Amino acid and mass‐spectrometry analyses showed that these new components consist of dimeric cross‐linked muropeptides lacking one of the two disaccharide (N‐acetyl‐glucosamine‐β‐(1→4)‐N‐acetyl‐muramic acid) molecules. This unique structure suggests an active role for an N‐acetyl‐muramyl‐l‐alanine‐amidase in remodelling the peptidoglycan of intracellular S. typhimurium. Additional alterations observed included: (i) the absence of glycine‐containing muropeptides; (ii) the increase in the relative proportion of muropeptides cross‐linked by l(meso)‐diaminopimelyl‐d(meso …