The cloud point curve for blends of poly(dimethyisiloxane) (PDMS, M-w = 2.5 kg mol(-1)) and poly(hexyl methylsiloxane) (PHMS, (M-w = 113 kg mol(-1)] was determined turbidimetrically. The system demixes upon cooling and the UCST amounts to 36 degrees C. The interfacial tension gamma was determined at the critical composition for three temperatures by means of a spinning drop tensiometer. The dependence of gamma on the reduced critical temperature can be described within experimental error by both the mean field theory and the Ising-3D theory.