Radiometry at the water vapour line with a scanning antenna beam from horizon to horizon through the zenith, in the vertical plane, was shown to be useful in estimating the integrated water vapour content from the zenith angle variation of radiometric temperature. The beam scanning may be made at a rate slower than the radiometer time constant using a Dicke type radiometer. Alternativeiy, a fast scanning beam may be used in a total power radiometer with a synchronous detection of the radiometer output at the scanning frequency to obtain a space domain Dicke switching for the measurements. A simultaneous scanning beam with 22-235 and 31-4GHz radiometers would allow us to separate the liquid water, if any, from the integrated water vapour content. Theoretical studies of the scanning beam radiometer performance in the estimation of integrated water vapour content from radiosonde data is presented and some typical results of Dicke type scanning beam radiometers at 22-235 and 31-4 GHz are also presented in this paper. © 1993 Taylor and Francis Ltd.