The reduction of the direct product of two unitary irreducible representations of supersymmetry into a direct sum of UIR’s is carried out for the massive case, and the Clebsch–Gordan coefficients are written down. The supersymmetric coupling of the different spin components of a multiplet arises from the use of the ’’superhelicity’’ basis (superhelicity κ=−j0,−j0+1,...,j0−1,j0) in which the spin is not diagonal. Here j0=O,1/2,1,... is the ’’superspin,’’ and the ordinary helicity, λ, is given by λ=κ or κ±1/2. The physical results are retrieved by transforming back to the spin basis after the reduction. The results of the reduction are used to analyze the scattering processes 1→2+3 and 1+2→3+4 for particles belonging to supersymmetric multiplets. The ordinary partial wave helicity amplitudes are given in terms of a small number of reduced partial wave superhelicity amplitudes corresponding to given total superspin. By continuing the latter to complex superspin, it is shown how, in the high-energy limit in the crossed channel, a singularity in one superhelicity amplitude contributes to the high-energy behavior of several different spin channels.