Shear thickening is an intriguing rheological behavior which consists in a brutal increase in the viscosity above a critical shear rate. It is famously encountered in suspensions of corn starch in water. Despite having been discovered in the early 1930’s, its underlying mechanisms remained a mystery for a long time. In 2013-14, numerical and theoretical works [1,2,3] put forward a frictional transition scenario to explain this phenomenon. In this talk, I will present experimental work investigating this frictional transition scenario. In order to test the ideas of this model, one has to go further than standard rheological techniques, since they do not provide access to the frictional state of the measured suspension. I will therefore focus on the techniques that we developed in order to evidence the frictional transition and link it to the presence of a shear-thickening behavior.  R. Seto, R. Mari, J. F. Morris, and M. M. Denn, “Discontinuous shear-thickening of frictional hard-sphere suspensions,” Physical Review Letters, vol. 111, 2013.  R. Mari, R. Seto, J. F. Morris, and M. M. Denn, “Shear thickening, frictionless and frictional rheologies in non-Brownian suspensions,” Journal of Rheology, vol. 58, no. 6, pp. 1693–1724, 2014.  M. Wyart and M. E. Cates, “Discontinuous shear-thickening without inertia in dense non-Brownian suspensions,” Physical Review Letters, vol. 112, 2014.