This Phase II research will develop miniature dosimeters for measuring and recording the concentrations of toxic gases at very low levels. These dosimeters are of interest to researchers in the exposure assessment field, and will also find use in industrial hygiene. In this study, we will develop and test recording dosimeters for carbon monoxide, nitrogen dioxide, hydrogen sulfide, formaldehyde, and ethylene oxide. These dosimeters will employ miniaturized amperometric gas sensors and even smaller microfabricated sensors and will be capable of such sophisticated controlled-potential measurements as cyclic voltammetry. Phase I research has demonstrated that cyclic voltammetry using microsensors can be used to distinguish hydrogen sulfide from sulfur dioxide as well as giving quantitative information. Presently-available technology can be used to develop recording dosimeters that are less than 5 cubic inches in size and will accumulate data for at least a week.