TIROS II measurements of infrared radiation in the 10-micron “water-vapor window” on one orbital pass over the United States are examined in detail relative to the field of cloudiness as derived from TIROS II television pictures and from other meteorological data. The radiation data are found to portray clearly the large-scale systems of middle and dense high cloud overcast, a capability that exists both day and night. Through use of information about the vertical and horizontal temperature fields, useful quantitative estimates of the heights of the tops of cloud systems are derived. In cases where there is a low overcast, the window measurements in themselves may not distinguish clouds from clear areas; but during daytime if television pictures are available, the window measurements can clearly show where a cloud overcast is low in height. Some tentative conclusions about the partial transparency of cirrus clouds to infrared radiation are also presented.