Cell suspension cultures of Catharanthus roseus were used to study the effect of temperature on plant cell lipids and indole alkaloid accumulation. Lowering the cultivation temperature increased the total fatty acid content per cell dry weight relative to that at higher temperatures, mainly because of increased accumulation of unsaturated C18 acids. In addition, an increase in the relative proportion of phosphatidylcholine and phosphatidylethanolamine was observed. Within individual lipids, the degree of unsaturation was increased and the mean fatty acid chain length decreased with reducing temperature. These changes may be interpreted as modifying the cell membrane fluidity to keep it optimal for growth and metabolism at each temperature. In spite of membrane modifications, the indole alkaloid content of the cells or the medium was not affected by temperature change.