The Is core-level absorption spectra of the sp(3) bonded carbon (cubic and hexagonal polymorphs) and boron nitrides (zincblende and wurtzite polymorphs) were calculated using an ab initio pseudopotential plane wave method including the core-hole effects. A comprehensive comparison with the available experimental data shows that there exist characteristic features that can be used to spectroscopically identify the different polymorphs. The anisotropic characters of K-edge absorption spectra in hexagonal diamond and wurtzite boron nitride can provide additional phase specific signatures. The application of the spectroscopic fingerprinting method in the experimental identification of these metastable sp(3) bonded phases is discussed. (C) 2004 Elsevier B.V. All rights reserved.