The precipitation of the compound FeSn from strongly supersaturated α-FeSn solid solutions takes place in a discontinuous reaction of the dislocation type. The effect of third alloy components on the morphology and kinetics of the precipitation process was studied. The following third alloy components in concentrations ranging from 0,3 to 2 at.% were added to an FeSn alloy containing 8 at.% Sn: phosphorus, silicon, germanium, gallium, zinc, copper, cobalt, manganese, chromium and vanadium. The results were discussed using various models. It could be shown that the effect of the valence difference between the third element and iron on the volume diffusion process is chiefly responsible for the deviation of the precipitation kinetics from that binary α-FeSn alloys.