Fourier transform infrared (FT-IR) spectroscopic imaging with focal plane array detectors has proved a powerful technique for rapid chemical visualization of samples, with a lateral resolution up to 10-15 microm in the transmission micro mode. In the present communication the application of this technique is described for the study of the diffusion of D2O into a polyamide 11 (PA11) film. Apart from the in situ visualization of the diffusion front propagation in the time-resolved FT-IR images, the type of diffusion and the diffusion coefficient of D2O in the investigated polyamide have been determined.