The structure of radioactive beams is investigated using the simplest possible probe: the proton used as a target in inverse kinematic reactions. From (p, p′) reactions, information on the neutron and proton transition densities is obtained through the comparison between the measured inelastic cross sections and the ones calculated using a microscopic potential and theoretical densities. (p, p′) inelastic scattering data to the first excited state for the halo nucleus 6He and for other nuclei 34Ar and 34,36S have been measured at GANIL using the MUST telescopes. This allows one to extract the global features of the transition densities, as shown for the halo nucleus 6He. We can also probe the evolution of the shell structure along isotopic chains in moving towards the neutron or proton drip lines. The example of the sulfur isotopic chain is discussed.