Sweat pores on the epidermal ridges are hypoplastic and reduced in number in three sisters affected with autosomal recessive hypohidrotic dysplasia. The heterozygote state is expressed by a reduced number of qualitatively normal sweat pores (14.07 +/- 8.59 as compared to 22.27 +/- 2.33 in controls). Clinical and genetic considerations suggest that this may be a distinct type that has to be differentiated from other autosomal recessive hypohidrotic ectodermal dysplasias. Heterozygote manifestation may contribute to delineate this groups of disorders further.