The LPS patterns of 231 H.p. strains were studied by using SDS-PAGE. The strains were isolated from the nasal mucous membrane of clinical healthy animals, from animals with GK and from animals with pneumonia without any symptoms of GK. The LPS patterns of H.p. strains consists of 2 to 4 bands of high electrophoretical mobility. In all it was possible to distinguish seven different LPS electrophoretic profiles. The distribution of the H.p. isolates from clinically healthy animals and animals with GK or pneumonia to the 7 LPS electrophoretic profiles shows a similar picture. Variation in the growth conditions showed a process of a standardization of the LPS structure as a result of an increased CO2 atmosphere or lack of O2 respectively.