JET equipped with ITER-like wall (a beryllium wall and a tungsten divertor) can provide auxiliary heating with power up to 35MW, producing a significant population of a-particles in DT operation. The direct measurements of alphas are very difficult and a-particle studies require a significant development of dedicated diagnostics. JET now has an excellent set of confined and lost fast particle diagnostics for measuring the a-particle source and its evolution in space and time, a-particle energy distribution, and a-particle losses. This paper describes how the above mentioned JET diagnostic systems could be used for a-particle measurements, and what options exist for keeping the essential a-particle diagnostics functioning well in the presence of intense DT neutron flux. Also, a-particle diagnostics for ITER are discussed.