[en] The exponent eta for the temperature dependence of the self-broadening coefficient of carbon monoxide has been measured directly using a tunable diode laser spectrometer. For lines of 12C16O between P(25) and P(31), the exponent has a value of 0.66 +- 0.05. For the P(13) and P(16) lines of 13C16O, the exponent appears to be the same. These results show that the value of eta is less than the generally accepted value of 0.75 for temperature between ambient and 180 0C