Measurements have been made on the rate constants for the stepwise excitation SE of the e³σ and b³σ states of CO from the a³π metastable state of CO. The measurements were made in the positive column of a discharge in a mixture of He + 0.1% CO by the use of a heating pulse superimposed on the decaying plasma. It is shown to be possible to distinguish the direct excitation from the stepwise and to extract information on the SE cross sections for these states.