Whole body sweat rate in two brothers suffering from congenital ectodermal dysplasia (CED) was measured. At a moderate heat load (DBT 30° C and 50% relative humidity) the authors found no apparent weight loss due to sweating. At a higher heat load (DBT 36° C, 50% relative humidity) sweating was observed, but only at levels approximately two thirds of those observed in normal controls. In the light of these experimental results, the authors support the suggestion that the nomenclature for CED patients should be changed. Instead of the present classification of anhidrotic CED and hidrotic CED, it is suggested that the terms hypohidrotic and hidrotic be substituted.