A CO2 laser was used to measure the ratio of line strength to line width for a great number of rotational lines in the 9.4-μ and 10.4-μ bands of CO2. The laser used for this purpose incorporated a grating, which allowed the tuning of the laser to about 100 different rotation lines. By assuming a given value of the line strength of the line P(20) in each of the two bands studied, the line width was calculated up to a rotational quantum number J = 40. These results are compared with other values recently reported in the literature. © 1969 Optical Society of America.