An indole alkaloid mixture, obtained from the leaves of Catharanthus roseus, was analyzed by means of supercritical fluid chromatography (sfc) in conjunction with ms. Under the conditions employed, a completed chromatogram was obtained within 8 min with an estimated 40 alkaloids being detected when a uv monitor was employed. By using a mass spectrometer in thermospray filament-on mode in conjunction with the uv monitor, an estimated 60 alkaloids could be detected. When the chromatograph was coupled to a mass spectrometer in ei mode, high quality ei mass spectra were obtained, which in turn allowed for the identification of several alkaloids. Monoterpene indole alkaloids represent a large and diverse family of natural products whose members occur mainly in plants belonging to the families Apocynaceae, Rubiaceae, and Loganiaceae. Separation and characterization of these alkaloids in plant extracts can be an imposing problem due to the large number and very different amounts of components normally present in an extract. Moreover, the alkaloids possess a wide range of solubilities, molecular weights, and polarities, factors which, although providing the basis for analytical separations, can also limit the utility of various techniques when one considers the overall separation. TLC has proven to be a useful method for their separation, while use of spray reagents in conjunction with tlc has proven a sensitive method for their detection (1). Reversed-phase hplc using gradient elution has also been used with some success (2,3). Unfortunately, both of these techniques have shortcomings; tlc spots obtained from polar compounds sometimes overlap. Furthermore, identification of unknown alkaloids separated by tlc is not possible using spray detection. Co-elution of components is also common when using hplc for the separation of these compounds (4). Diode array detection is useful for the confirmation of specific alkaloids as well as for studying co-eluting peaks but is of limited use for characterizing unknown components (5). Traditionally, much structural information has been obtained from ms of individual alkaloids isolated from complex mixtures of plant material using relatively large scale extraction and cc methods. Large scale separations of plant material require a significant number of manipulations which in turn increases the probability of artifact formation. Recently, supercritical fluid chromatography (sfc), a technology well suited to interfacing with a mass spectrometer, has been shown to be more efficient than hplc and has proven effective in analyses of various polar compounds, including mixtures of ergot alkaloids (6). Accordingly, as a potentially useful means of directly obtaining pertinent information on the number and type of monoterpene indole alkaloids in a relatively small amount of complex sample, we sought to evaluate the use of sfc-ms using an alkaloid mixture obtained from the leaves of the medicinal plant Catharanthus roseus G. Don. (Apocynaceae). C. roseus is one of the most thoroughly investigated of plants with regard to its constituent indole alkaloids, of which more than 70 have been isolated from the whole plant (7). A description of the technique is presented below.