The concentration of atmospheric carbon dioxide at and near Mauna Loa Observatory, Hawaii, is reported for the first six years (1958-1963) of a long-term program to document the effects of the combustion of coal and petroleum on the distribution of CO2 gas in the atmosphere and in the world's oceans. The majority of the measurements reported here were obtained at Mauna Loa Observatory with a continuously recording infrared gas analyzer. Also reported are measurements of 261 discrete samples of air collected in glass flasks on Mauna Loa, on the windward coast of Hawaii, and from aircraft near the Hawaiian Islands. The following results have been obtained: (1) The CO2 concentration at Mauna Loa Observatory varies with season with an average amplitude of 6 ppm and is increasing at the average rate of 0.7 ppm per year. (2) These variations reflect regional changes in the air which lies above the trade wind layer near Hawaii. (3) The concentration of CO2 in the trade wind layer is essentially the same as aloft except during the summer months when it is slightly lower. (4) Volcanic emanations of CO2 near the summit of Mauna Loa and uptake of CO2 on the forested lower slopes of the mountain influence the concentration of CO2 at Mauna Loa Observatory but do not seriously interfere with the determination of regional changes.