Many gram negative bacteria accumulate cyclopropane fatty acids (CPFAs) in their membranes during stationary phase. In plants, on the other hand, CPFAs are best known as constituents of certain seed oils. CPFAs make up around 40% of Litchi chinensis seed oil [1] and a significant proportion of oils from other Sapindales. In order Malvales, small amounts of CPFA typically accompany cyclopropene fatty acids in seed oils, although up to 5% CPFA has been observed in the polar lipid fraction from Malvaceous roots [2]. Genetic engineering of oilseeds for unusual fatty acid production requires that the introduced fatty acids accumulate in triacylglycero1 without compromising membrane structure or function. A major purpose of this study has been to determine whether a higher plant would express a bacterial CPFA synthase, and, if so, how the resulting CPFA would be partitioned.