In-line rheo-optical techniques are a quantitative set of experiments in which the behavior of the polymer melt flow, known as rheology, is measured at the same time as effects due to the interaction of the light with the polymer melt. In the first case the pressure drop along a specific path, with a particular shape and dimension is recorded. In the second case light absorption, light scattering and structure anisotropic effects in the light propagation velocity (birefringence) are measured. For this porpoise we have design and constructed an instrumented slit die with various features which enables it to get all variables mentioned in real time. The slit die has three ports to measure pressure along the slit and two transparent windows to allow for the optical measurements including turbidity and birefringence. This instrumented die is fixed at an extruder exit, a way to provide a particular flow of polymer melt. Using different polymer blends and processing conditions all rheo-optical variables can be obtained and the intrinsic and morphological characteristic of the polymer melt be studied. The results can be compared with any conventional off-line measurement like, thermal (DSC), spectroscopic (FTIR), morphology (POM, SEM, TEM), taken from samples removed during the extrusion. Examples of various set of data will be presented during the conference, including pure polymer and diluted polymer blends.