Time series data of atmospheric CO2 concentrations are presented for three Canadian background stations: Ocean Weather Station P in the northeast Pacific Ocean, Sable Island off Nova Scotia, and Alert, Northwest Territories. The mean annual concentration of CO2 in dried samples of 338.73 parts per million by volume (ppmv) (1980) at Sable Island, 337.26 ppmv (1980) at Station P, and 340.30 ppmv (1980) and 341.71 ppmv (1981) at Alert appear consistent with the global pattern. From 1975 to 1981, the increase in CO2 concentration averaged for these stations is 1.4 ppmv/yr. In 1975-1976 and in 1978, the annual growth rates of atmospheric CO2 measurements decreased at all stations. Another dip in the growth rate of CO2 concentrations was also observed in 1974-1975 at Station P. In general, the long-term trends all show lower growth in the beginning, and more rapid growth at the end, of a typical 2-year El Nino/Southern Oscillation event. The seasonal amplitude between winter and summer concentrations is about 14 ppmv at Station P and about 15 ppmv at the other stations. There is a phase shift of about 1 month in the onset of the decline to summer minimum between Sable Island (March-April) and the other stations (April-May).