1. In cobalt 60 teletherapy the skin sparing effect can be enhanced, for all field sizes and filter-skin distances, by use of a leaded glass electron filter having a density of at least 3.2 gm./cm.3. This will result in a 20-30 per cent decrease in relative skin dose over a lucite filter on the open beam. Leaded glass filters are as effective as pure metals in reducing the skin dose. The filter thickness needs to be just sufficient to stop all electrons arising on the source side of the filter. 2. The relative skin dose depends upon the field size and, to a lesser degree, upon the filter-skin or collimator-skin distance. Whenever a leaded glass filter is used the relative skin dose can be predicted from the expression, See PDF for Equation where h is the filter-skin on collimator-skin distance and r is the effective radius of the field on the skin. 3. The common belief that optimum skin sparing is achieved whenever the filter-skin distance is at least 20 cm. does not hold for the larger field sizes. Whenever skin sparing is important the value of h/r should be as large as possible, and should be at least 2 when a leaded glass filter is used. For field sizes of 5x5 cm., 15x15 cm., and 30x30 cm. this requires filter-skin distances of 6 cm., 17 cm., and 33 cm., respectively.