Trans-Neptunian objects (TNOs) are considered some of the most pristine objects in the Solar System. Their surfaces display a wide range of compositions, going from surfaces covered by dark irradiation mantels, to surfaces totally covered by ices. According to models of the retention of volatiles, only TNOs with a diameter d &gt 1000 km are expected to retain any of their original complement of volatile ices on their surface. However, surface refreshing processes on smaller bodies (e.g., collisions, transient atmospheres and cometary activity) could bring to the surface some amount of ices that are stable at depth. When these processes affect only part of the surface they cause surface heterogeneity. The study of rotational variability of medium and large sized TNOs is important to better understand the physical processes affecting their surfaces, and if these processes are local in scale or, on the contrary, extend across the whole surface. We present rotationally resolved spectroscopy of two TNOs, (20000) Varuna and (136472) Makemake. Varuna is a medium sized TNO ( 621 km). We observed Varuna with NICS@TNG telescope, in the NIR, covering two entire rotations of the object. The analysis of the data shows a homogeneous surface composed of a mixture of complex organics, silicates and water ice. Our data also indicate an upper limit of 10% of methane ice on the surface. The Dwarf Planet Makemake is also studied in this work. The surface of this large TNO shows that, similar to Pluto and Eris, it clearly retains large amounts of volatile ices. Moreover, thermal observations indicate that Makemake has a heterogeneous surface that could be the result of volatile migration. We present new visible spectra of Makemake, obtained with ISIS@WHT telescope, covering 80% of the surface. We present a detailed study of the differences in the absorption bands across the surface that are indicative of changes in the relative abundances of ices, temperature, and/or particle size. Moreover, we collect all data available from literature, after 8 year from the discovery of Makemake, and compare with our data to investigate possible rotational and secular variations.