The past decade has witnessed the development of a novel class of tools for environmental monitoring: genetically engineered microorganisms 'tailored' to respond in a dose-dependent manner to changes in environmental conditions. Recent advances in the field include the expansion of available reporter functions with multicolored fluorescent proteins, a broadening of the detected chemical effects such as the availability of nutrients and enhancement of the spectrum of reporter microorganisms to include cyanobacteria, yeast and fungi. Most importantly, the stage has been set for the incorporation of such cells into various whole-cell array formats on silicon chips, optic fibres and other configurations. The future of such multiplex detection and analysis systems seems bright.