A theory for the coalescence of droplets dispersed in molten quiescent polymer blends has been derived. The theory is based on the idea that, in blends with a higher content of the dispersed phase, a great part of the dispersed droplets are located in the close vicinity of other droplets. Drainage of the liquid him of the matrix between the colliding droplets is the decisive step in coalescence. The time dependences of droplet radius for systems with different interface mobilities and driving forces for coalescence have been compared. It has been shown that different combinations of interface mobility and driving force can lead to the same shape of the time dependence of droplet radius. The theory predicts a somewhat higher rate of coalescence than that which has been determined experimentally. It follows from the discussion of commonly used expressions for the coalescence time with partially mobile and immobile interfaces that these expressions fail in the case of a weak driving force for coalescence. The derivation of more adequate expressions for systems with a weak driving force for coalescence is necessary for a further improvement of the theory.