In our laboratory, we are investigating the detection of gas-phase species using tunable diode lasers coupled with wavelength modulation or cavity ring-down detection of absorption signals. In both sets of experiments, we use an external cavity diode laser, which is tunable between 1507 and 1582 nm. NASA has identified a select group of target compounds to be monitored in spacecraft air that include major and trace species. Major species include both the principal components of the air, but also several species that represent toxic or explosive hazards to the crew. Many of the molecules on the NASA priority lists are molecules with transitions in the 1550 nm vicinity. In this paper, we will discuss the detection of carbon monoxide, carbon dioxide, water, acetylene, hydrogen cyanide, and ammonia using this laser system.