Irradiation induces the formation of stacking fault tetrahedra (SFTs) in a number of fcc metals, such as stainless steel and pure copper. In order to understand the role of the material's parameters on this formation, pure Cu, Ni, Pd and Al, having a respective stacking fault energy of 45, 125, 180 and 166 mJ m(-2), have been irradiated with high energy protons to a dose of about 10(-2) dpa at room temperature. The irradiation-induced microstructure has been investigated using transmission electron microscopy. All irradiated metals but Al present SFTs. The proportion of perfect, truncated and grouped SFTs has been determined. The SFT energy as a function of size has been calculated using elasticity of the continuum, with respect to the energy of a number of other possible defect configurations. It appears that the key parameters are the stacking fault energy and the shear modulus. Their implication on the formation and stability of the SFTs is discussed.