The development of monitoring devices that can be operated while attached to an ambulatory individual is discussed. Two have been selected for more detailed study and development. A preliminary report of tests performed with one instrument equipped with impregnated silica-gel tubes and controlled air flow for collecting and measuring nitrogen dioxide, sulfur dioxide, total hydrocarbons, and carbon monoxide, together with a filter disc to capture particulates, is offered for discussion. The first phase of development of a second device using silica-gel pack from which the gases could be desorbed and analyzed by gas chromatography is also presented. The schematic assembly of components is described for each of these devices.