From January 1977 through May 1978 atmospheric CO2 concentrations were measured hourly and/or continuously at bimonthly intervals over periods varying from 5 to 8 days at 10 different locations in Kenya, East Africa. During each of these periods, at least two, and in some cases five, vertical profile measurements of CO2 concentrations were conducted above different biomes. A large diurnal CO2 periodicity was observed over land, with daytime drawdowns to 322 ppm and nighttime buildups to more than 400 ppm observed in savannah regions. In and around tropical rain forests, drawdowns to 310 ppm and buildups to more than 400 ppm were regularly observed. On the higher reaches of Mount Kenya, the diurnal CO2 cycle was considerably reduced in amplitude, with variations in the range of 2--6 ppm throughout the 16-month study period. On sunny days, the drawdown of CO2 was measurable to heights of at least 4000 m above ground level. Other CO2 concentration measurements in air over the Indian Ocean (to distances of up to 450 km upwind of the coast) produced fairly consistent concentrations of about 328.5 ppm which did not fluctuate diurnally. The weekly mean CO2 concentrations over Kenya appear to have a bimodal structure, with minima occurring in July and January. On the basis of the data collected during the study it appears likely that regular observations at a high-altitude station on Mount Kenya, either with flask sampling or continuous analyzer measurements, are likely to yield data useful for estimates of CO2 concentration backgrounds and trends. Also, there is strong evidence that Mount Kenya would be a good location to measure large-scale interhemisphere CO2 exchanges and provide a unique base from which to study the effects of the tropical biome on biogeochemical phenomena.