Obtaining local experimental data in internal rarefied gas flows is still a challenge. Most of the current data are relative to mass flow rates and inlet/outlet pressures for channel flows, or to local temperature and pressure measurements at the wall by microsensors or sensitive paints, but there is a crucial need for investigating velocity and temperature fields directly within the gas in a non- or at least low- intrusive manner. This talk presents recent developments of the molecular tagging technique developed for velocimetry and thermometry purposes in confined and rarefied gas flows, using acetone vapour as a luminescent molecular tracer. Velocity profiles are obtained in a pressure driven slip flow through a rectangular mini-channel in low-pressure conditions. Measured displacement profiles are used to reconstruct the velocity profile, taking into account molecular diffusion. Velocity slip is observed and measured at the wall. The potential of the technique for thermometry is also investigated, and it is demonstrated that temperature mapping is possible, thanks to the sensitivity of tracer luminescence signal to the tracer number density, which can be linked to the temperature in uniform pressure conditions. The current limits of molecular tagging velocimetry (MTV) and thermometry (MTT) are discussed and perspectives to improve this promising experimental tool are proposed.