Experimental results are presented which show that the dynamic Stark effect significantly reduces the small‐signal gain (in discharge‐excited CO2) and absorption (in unexcited CO2) at the line center of 4.3‐&mgr;m laser lines directly coupled to 10.4‐&mgr;m sequence‐band pump transitions. In unexcited CO2, population transfer by the pump radiation is negligible and the influence of coherent effects can be observed unambiguously. The results of comparing experiment and theory in this simple case are used to modify a rate‐equation model of the 4.3‐&mgr;m gain dynamics, and the modified calculations are shown to be in good agreement with measured 4.3‐&mgr;m gain coefficients.