The secular increase of the total vertical column abundance of carbon monoxide has been derived from sets of infrared solar spectra recorded from an altitude of 3.58 km at the Jungfraujoch Station, Switzerland, in 1950–1951 and in 1985–1987. The results are based on equivalent width measurements of the R3 line of the 1-0 vibration-rotation band of 12C16O at 2159.30 cm−1. The set of 1985–1987 observations indicates a strong seasonal cycle in the total column abundance of CO, with a ±25% modulation between minimum values in late summer and the maximum values in late winter. Variability on shorter time scales is also present in both the old and recent data sets. The mean cumulative rate of increase of the total column abundance of CO above the Jungfraujoch is found to be (0.85 ± 0.20)%/yr between 1950–1951 and 1985–1987. The present findings are compared with trends reported in earlier studies.