A symmetry X optical setup has been developed for the absolute measurements of reflectance and transmittance of a specular sample. Both the transmittance spectra and the geometric mean of the reflectance spectra were measured within the uncertainty of +/-0.4%, respectively. The solution of two simultaneous equations with the measured reflectance and transmittance determines the optical conductivity of the sample. The conductivity by the new method is compared with that by the ordinary method using Kramers-Kronig relations. (C) 2003 Elsevier Science B.V. All rights reserved.