Results of investigations by scanning FT-IR microscopy carried out to estimate the interdiffusion coefficients across the interface boundary of contacting compatible polymers are reported. It is shown that the methods can be used to provide evidence for the evolution of concentration-way profiles along interphases developed during interdiffusion of miscible components of contacting polymers. The data obtained for the contacting polymer pairs assembled of poly(styrene-b-methylmethacrylate) diblock-copolymer with poly(2,6-dimethyl-1,4-phenylene ether) and poly(styrene-co-acrylonitrile), respectively, are presented. In the former contacting polymer pair, PPE is compatible with the PS block, whereas in the second pair, the PSAN copolymer is compatible with the PMMA block of the block copolymer. Almost symmetrical concentration-way profiles across the interface point at constancy of the interdiffusion coefficients, which are of the order of 10(-12) cm(2)/s. The data obtained suggest additionally that the interdiffusion coefficients are dependent on molecular weight.