The application of diode-laser-pumped tunable IR sources to trace gas detection in air is discussed. The design and technology issues of CW tunable mid-infrared difference-frequency generation are addressed. Feasibility experiments are reported in which the detection of CH\sb4, and CO was performed at low pressure and in air using two laser sources near 3.2 μm, and 4.7 μm, respectively. They were based on difference-frequency mixing in AgGaS\sb2 at room temperature. Pump sources used were a diode-pumped Nd:YAG laser at 1064 nm, a laser diode at 693 nm, and a tunable fiber-coupled Ti:Sapphire laser near 795 nm, and 813 nm. Detection limits of 2.4 ppbm/Hz for CO, and 9.0 ppbm/Hz for CH\sb4 in air are estimated for 0.1 μW of IR probe power based upon the performance of the sources and detector.