Procedures for sample clean-up and concentration in Capillary Zone Electrophoresis (CZE) have been developed for determination of drugs in biosample s. An on-capillary concentration technique based on enhanced field strengths, the double stacking procedure is introduced. This procedure allows for concentrationg all cations in the sample several hundred times essentially without loss of separation performance. This technique is fully comptible with the clean and low ionic strength extracts obtainable from treating plasma samples with the novel supported liquid membrane (SLM) sample pretreatment technique. Both off- and on-line approaches are presented for the combination of the SLM technique with the double stacking CZE. In the simplest approach the SLM technique is used in an off-line combination with ZCE. Only a part of the SLM extract is used for the final analysis by CZE and the enrichment factor obtained is more than 1000 times. In another approach a comparable enrichment factor was obtained by connecting a minituarized SLM device on-line with CZE. The whole extracted sample volume could now be injected into the CZE capillary. In the third approach the SLM device is connected via a CLC-microcolumn system on-line to the CZE system. This system being the most complicated one gives enrichment factors around 40 000 times and very high selectivity towards matrix components. Cyclodextrins were explored for the separation of enantiomers of drugs. The chiral separation systems were compatible with the CZE double stacking procedure and were used for the determination of drug enantiomers in biosamples.