In this analysis of membrane lipid compositions in Helicobacter pylori, the membrane lipid profiles drastically changed during coccoid formation: cholesteryl-6-O-tetradecanoyl-α-D-glucopyranoside levels increased, cholesteryl-α-D-glucopyranoside and phosphatidyl ethanolamine decreased, and a coordinated increase in cardiolipin and decrease in phosphatidyl glycerol were observed. Cholesteryl-6-O-phosphatidyl-α-D-glucopyranoside was hardly detected in the spiral forms in the logarithmic phase, but subsequently increased throughout the coccoid conversion. These results suggest that environmental stresses induce the expression of certain regulatory systems for lipid metabolism in H. pylori, and that the resulting alterations in lipid composition play an important role in inducing the coccoid conversion. © 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.