The inclination angle of a transparent material exposed to solar radiation strongly varies depending on the application. It is well known that the inclination angle can highly influence the shape of condensation drops-which are sometimes unavoidable in solar thermal applications-via its effect on the receding and advancing contact angles of the drops. By means of a laboratory set-up, the effect of condensate on the transmittance of 25degrees and 90degrees (i.e., vertical) inclined single glass, polyethylene and anti-drop condensation polyethylene was measured for incidence angles up to 45degrees. No significant impact of the inclination angle on the transmittance of the three transparent materials in the wet state was observed. This means that transmittance results, obtained on wet materials can be applied irrespective of the inclination angle of the material. (C) 2002 Elsevier Science B.V. All rights reserved.