Yersinia enterocolitica S and R strains change the pattern and the amount of their lipopolysaccharide-linked fatty acids with the respective growth temperature. As described also for other enterobacterial strains, saturated fatty acids are decreased, especially the amount of C14:0, when growth was done at 10 degrees C and unsaturated fatty acids, notably C16:1 (palmitoleic acid), appear, which are present in trace amounts only when bacteria are grown at 40 degrees C. In addition to these changes in the fatty acids, also the amount of O-specific sugars is temperature-dependent. 6-Deoxy-L-altrose which is the only main O-specific sugar in the LPS investigated, amounts to 30-40% (based on LPS dry weight) when grown at 10 degrees C, but only to 13-20% when growth was done at 40 degrees C. The decrease in O-specific material at 40 degrees C can at least partly be explained by the finding of a high number of unsubstituted R core stubs in polyacryl gel-electrophoresis.