A tunable diode laser instrument denoted as DACOM (Differential Absorption CO Measurement) has been developed to meet the fast-response, high-precision CO measurement needs of the GTE (Global Tropospheric Experiment) program. Under the GTE program, DACOM participated in the three field missions of CITE 1 (Chemical Instrumentation Test and Evaluation 1), a project involving the intercomparison of trace gas measurement techniques. DACOM performance, including analyses of measurement error sources, is discussed for the ground-based mission at Wallops Island, Virginia (summer 1983), and two missions on the NASA CV-990 (fall 1983 and spring 1984). Examples of fast-response ( ≈ 1 s), high-precision (¿ 1 part per billion by volume, ¿ 1.5% of reading) airborne data are included to illustrate the capability or this instrument. ¿American Geophysical Union 1987