The dynamic loss of a cw dye laser was determined by measuring input‐output curves at a fixed wavelength for a variety of wavelengths. The actual losses were obtained from the constants of the straight‐line fits for plots of threshold power vs the negative logarithm of the output reflectivity and the inverse slope efficiency vs the inverse of the output mirror transmission. A simplified kinetic‐dynamic model of the cw dye laser has been developed to interpret the experimental data. The model is consistent with experiment in the interpretation of the loss information and, with the use of reasonable molecular constants, is also consistent with the dependence of threshold power on the output reflectivity. The actual loss measured is different, at the shorter wavelengths of oscillation, for the two approaches. This difference arises because the population‐dependent losses (singlet and triplet absorption of the intracavity laser flux) contribute differently to the efficiency and the threshold. At the longer wavelengths (> 6000 Å) of oscillation these contributions to the loss become very small and the residual scattering, reflection, and diffraction losses remain. The simplified model is successful in dealing with the loss and threshold data and a measure of the triplet‐triplet absorption constant can be obtained by combining the kinetic analysis and fitting the threshold power data. The model is less successful in the area of efficiency and this appears to be related to some of the approximations used. A single numerical correction factor, however, brings the efficiency data into reasonable agreement with the model.