High energy ball milling of powders involves successive events of fracture and welding promoting mechanical alloying, fine and homogeneous dispersions could be attained. To minimize excessive cold welding during milling of ductile particles, the so called process control agents (PCAs) are added to the powder charges. These additives, mostly organic compounds, act as a coating of the particles inhibiting welding. It is known that PCAs are a source of contamination, so under this point of view its quantity much be the lowest possible. Moreover performing combustion synthesis of a powder mixture with PCA requires a pretreatment during the heating for extracting the PCA before reaction takes place, otherwise it can impair densification. In this work the use of stearic acid as PCA in milling Nb-Al and Ni-Al powder mixtures was investigated. The aim was to find a optimum quantity of that additive concerning milling action and decreased contamination.