We have studied the stability of mixed (3)He/(4)He clusters in L=0 states by the diffusion Monte Carlo method, employing the Tang-Toennies-Yiu He-He potential. The clusters (3)He(4)He(N) and (3)He(2)(4)He(N) are stable for N>1. The lighter atoms tend to move to the surface of the cluster. The minimum number of 4He atoms able to bind three 3He atoms in a L=0 state is nine. Two of three fermionic...