Capillary zone electrophoresis (CZE) is a new powerful analytical separation technique which provides special selectivity, extreme sensitivity, short separation times, small sample requirements, and practically no waste production. In spite of these advantages, only a small number of papers have been published describing the application of CZE to the separation of natural plant constituents (1, 2). In this presentation, the CZE separation of the main oxindole alkaloids from the root bark of Uncaria tomentosa (Willd.) DC. (Rubiaceae), namely pteropodine, isopteropodine, mitraphylline, isomitraphylline, speciophylline, and uncarine F, is reported. So far, analytical assays of oxindole alkaloids have been accomplished by TLC, GLC, and HPLC (3—5). The application of the published chromatographic methods to the separation of the stereoisomeric oxindole alkaloids from Uncaria tomentosa, however, gave unsatisfactory results. The chromatographic parameters for the presented CZE separation of the six alkaloids were optimized by studying the impact of the buffer composition, the ionic strength, the pH, and the applied electric field on the separation efficiency of the analytical system. Baseline separation of the alkaloids was achieved in less than 15 minutes using a fused silica capillary tube with a phosphate buffer (20mM, pH 5.6) as running electrolyte at a constant voltage of 10 kV. UV detection was performed at 254nm. The validity of this method was shown by application of CZE to separation and quantification of the oxindole alkaloids in a crude methanolic extract of Uncaria tomentosa (external standardization; standard deviation 2.57%; n= 6). The main anthrone constituents of Rhamnus purshiana DC extracts are cascarosides A (1, 1OS) and B (2, bR), earlier isolated by preparative paper chromatography, and cascarosides C and D, which have not yet been isolated in a pure form and fully characterized (1— 5). A method for the isolation of pure cascarosides A— D is now described and the structures 3 and 4 are assigned to cascarosides C and D on the basis of their spectral properties. Two main fractions (cascarosides A/B and C/D) were obtained from a commercial cascara extract by purification with n-BuOH followed by XAD-4 and silica gel column chromatography. Pure cascarosides A, B, C, and D were then isolated by preparative HPLC. Previous mass spectrometric studies on 1 with positive NH3/CI did not afford reliable information on the structure (6) and only with FD (1—3, 6) was the molecular ion obtained. On the other hand, negative NH3/DCI mass spectra of 1—4 afforded molecular ions and diagnostic fragmentations.