In the present work, the effect of different surfaces on the lyotropic nematic-isotropic liquid phase transition temperatures in nematic-calamitic and nematic-discotic mesophases and also on the character and temperature width of the heterophase region for these phase transitions has been investigated. The shift of the lyotropic nematic-isotropic liquid phase transition temperatures to the lower values and a change in width of the temperature range of the heterophase regions under the influence of surfaces have been found. (C) 2002 Elsevier Science B.V All rights reserved.