Introduction: Legionnair's disease bacterium is a gram negative, facultative intracellular bacilli which parasitize human alveolar macropages as well as some species of free living amobae. This study was achieved in order to compare the cell wall composition in intracellular bacteria. Whole cell and outer membrane proteins and the bacterial lipopolysacharide (LPS) were analyzec on SDS page system and immunoblot. Materials and Methods: L. pneumophila were originally isolated from pneumoina patients suferring from legionnaires' disease. Legionella were grown intracellularly under different tempratures. Bacteria were then released from host cellsand outer membrane proteins and LPS were extracted. Purified LPS and OMP along with cell envelope were sujected to SDS PAGE analysis. The proteins and LPS patternswere finally compared with cell components grown on the culture media different temperatures. The proteins patterns were reacted with L. pneumophila polyvalant antisera in western blot system. Results: The LPS patterns showed minor changes under different conditions of cellgrowth. The quantity of some LPS bands were also changed when extra and intra -cellular bacteria were compared. The OMP patterns also showed some major heterogeniticity under cell growth conditions. Interestingly, a new 15 Kda protein have been expressed in OMP patterns under intracellular growth. The western blot analysis revealed new protein to react weakly with anti-legionella antibody. Conclusions: It is postulated that some of molecular changes under intracellular conditions may contribute in legionella virulence in host cell.