1 Chair of Microbiology, Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Vecna pot 111, 1000 Ljubljana, Slovenia 2 Chair for Microbiology and Biotechnology, Department of Animal Science, Biotechnical Faculty, University of Ljubljana, Groblje 3, 1230 Domzale, Slovenia The membrane fatty acid composition of Escherichia coli becomes conditioned during periodic temperature cycling between 37 and 8 °C. After several cycles of temperature change, the bacteria become locked into a low-temperature physiology. Even after a prolonged incubation at high temperature the membrane fatty acid composition of conditioned cells was similar to that of cold-stressed cells. Correspondence David Stopar david.stopar{at}bf.uni-lj.si Abbreviations: ; C16 : 1, palmitoleic acid; C17 : 0cyc, methylene hexadecanoic acid; C18 : 1, cis -vaccenic acid; SFA, saturated fatty acid; UFA, unsaturated fatty acid