===================================================================== ==> In this proposal, more time is being requested for JCASSINE.PROP_BST ===================================================================== EUVE observations of two B stars show large Lyman continuum excesses which are naturally explained as temperature excesses in the extreme outer photospheres of these stars (Cassinelli et al. 1995; Cassinelli et al. 1996). Because the mid-infrared continua are formed at the same physical depths in B star atmospheres, such temperature excesses should also lead to IR excesses. We propose to use ISO (a) to better map out the Temperature-depth dependence in one of the EUV-excess B stars (beta CMa), and (b) to search for temperature excesses in other B stars, which are unobservable in the EUV. The ubiquity and nature of such photospheric temperature excesses have important implications for stellar atmosphere theory and for models of the galactic ionizing radiation field.