Plants produce a large family of natural compounds, isoprénoids, which are essential for a wide range of physiological functions including plant growth, development and reproduction. Most of enzymes involved in isoprenoid biosynthetic pathways have been characterized and their genes cloned. In the past few years, transgenic plants have been used in order to unravel the molecular mechanisms for regulation of isoprenoid biosynthesis. Various examples of such plants, carrying in addition agronomical advantages, have been reported. In spite of a possible horizontal dispersion of transgenes, such transformation experiments should be able to provide significant results on plant physiology.