The slowing-down process of suprathermal alpha particles in a rippled toroidal field is investigated by means of an orbit-following Monte-Carlo code. It is found that numerical results on the collisionless ripple loss agree fairly well with the theoretical predictions. The collisional diffusion coefficient for non-ergodic banana particles in a field ripple is derived. The ripple-enhanced power loss of alpha particles during slowing-down amounts to 10% of their total power in a reactor-grade tokamak with a toroidal-field ripple of δ ∼ 1%. The fraction of particle loss is 1.5 to 1.8 times as large as that of power loss. The ripple-enhanced banana drift dominates the alpha-particle loss process.