A miniaturized analytical system for separating and detecting toxic hydrazine compounds, based on the coupling of micromachined capillary electrophoresis (CE) chips with removable thick-ยฎlm amperometric detectors is described. The study also represents the ยฎrst example of using a chemically modiยฎed electrode for microchip CE applications. The microsystem with the electrocatalytic palladiumdeposited detector offers a rapid (2 min) low-potential ( 0.5 V vs. Ag=AgCl) simultaneous detection of hydrazine, methylhydrazine, dimethylhydrazine, and phenylhydrazine. Such compounds could be detected down to the 1.5610 ร6 M level, with linearity over the 2610 ร5 Mยฑ2610 ร4 M range examined. While the concept of miniaturized separation=detection systems is presented within the framework of hydrazine compounds, such devices should be attractive for ยฎeld monitoring of other classes of toxic contaminants. The design of the microsystem permits rapid replacement of the detector strip and a convenient surface modiยฎcation (in a separate, optimal cell). The development of fast-responding miniaturized systems, with negligible waste production, holds particular promise for meeting the requirements of ยฎeld `Green Analytical Chemistry'.