Measurements of tropospheric ozone have been made in the southern and middle California regions and over the Pacific Ocean during two series of flights in February and May 1977. The data were obtained by using a laser absorption spectrometer, a nadir-viewing instrument which remotely measures the ozone column abundance between ground level and aircraft altitude by interacting with ozone at specifice wavelengths near 9.5 μm. The measurements indicate significantly lower ozone abundances above the Mojave Desert region as compared with farm, forest, and urban areas. The average tropospheric column density was found to be 2.7¿10-3 atm cm/km over the Califronia region and 3.5¿10-3 atm cm/km over the Pacific Ocean region 1000-2000 km west of the coast of Mexico.