Near-infrared diode-laser-based systems using laser-absorption molecular spectroscopy can sensitively monitor atmospheric gases, pollutants, and toxic gases. They can also monitor trace gases on the human breath for medical diagnostics. The detection levels are equal to or less than parts per million. Sarnoff/SRI has made and tested room-temperature InGaAsP/InP DFB lasers operating at 1.39, 1.6, and 1.65 micrometers . All of these devices had output powers of 10 mW or more. The current-tuning rates varied from -580 to -1240 MHz/mA. The temperature tuning rate was about 0.1 nm/K for all devices. Continuous tuning ranges were 7 nm for the 1.39 micrometers lasers and 5 nm for the 1.6 and 1.65 micrometers lasers. We observed H2O at 1.39 micrometers , CO and CO2 at 1.6 micrometers , and CH4 at 1.65 micrometers . We monitored the ratio of 13CO2 to 12CO2 on human breath samples as the initial step towards clinical trials for medical diagnostics.