new technique for the study of the kinetics of adsorption of surfactants at the air-water interface on the 1-20 ms time scale is described. Ellipsometric measurements were performed directly on the surface of a high-speed jet containing a solution of hexadecyltrimethylammonium bromide (CTAB), The coefficient of ellipticity was converted to surface concentration with the aid of neutron reflection data obtained previously on an overflowing cylinder. By this method, the surface concentration in the jet can be measured with a precision of 5% of a monolayer. An approximate measure of the interfacial age was obtained from the speed of the jet. The experimental data were tested against theoretical predictions and found to be consistent with diffusion-limited adsorption within the error of the experiment. Experimental data obtained at different jet speeds were in good agreement, suggesting that Marangoni effects did not play an important role.