A new technique using fluorolabeled compounds as metabolic substrates is being developed to discover unknown intermediates in metabolic processes. Fluorine, functioning as a stable isotope heteroatomic lable, provides a novel and unique tool for detecting minute amounts of metabolic intermediates. Carbon-bound fluorine is detected using a microwave-induced plasma source for emission spectroscopy interfaced to a capillary gas chromatograph. Use of fluorine as a substituent also will provide fluorosubstrates that in some cases can be used as inhibitors of a specific metabolic process, serving two purposes: (1) causing the accumulation of an unknown intermediate to abnormally high levels, thus facilitating its identification; and (2) blocking the normal formation of a known intermediate, thereby enhancing the incorporation of its fluorolabeled analogue. The tagging and metabolic blocking capabilities of fluorinated analogues of normal substrates will be exploited to investigate the novel transformation of farnesyl pyrophosphate into cantharidin in blister beetles. Other experiments will seek to determine the origin of the oxygens in cantharidin. The results will provide insight into specific biochemical reactions and, ultimately, bond making and breaking events, revealing details about an unprecedented biosynthetic pathway for mevalonate-derived natural products. These results also will provide evidence regarding insect metabolism of farnesyl pyrophosphate, an important hormonal precursor.