Spectroscopy of organic molecules such as explosives in the terahertz (THz) regime can be used for identification by spectral fingerprinting. The ultimate goal of trace detection requires knowledge of the strengths of the absorption peaks as well as their locations. We report absorption cross-sections and absolute absorptivity for four explosives, TNT, RDX, HMX, and PETN, which allows calculation of the detection limit as a function of instrument signal-to-noise ratio. (C) 2007 Elsevier B.V. All rights reserved.