First, the method to calculate Coulomb collisions in materials processing plasmas is presented. Next, by use of the method, the effect of electron- electron (e(-)-e(-)) collisions on the relaxation of electron energy distribution function (EEDF) is examined for a spatially uniform argon plasma. The EEDF is shown not to tend to the Maxwellian distribution without e(-)-e(-) collisions because once high-energy electrons lose energy by inelastic collisions, they have no chance to recover their energy without e(-)-e(-) collisions. When e(-)-e(-) collisions are taken into consideration, the relaxation time of the EEDF at gas pressure 10 mTorr is 40, 20, and 10 mu s for electron densities 10(16), 10(17), and 10(18) m(-3) respectively. Lastly, the effect of e(-)-e(-) collisions on the EEDF is examined for a capacitively coupled plasma at gas pressure 25 mTorr. It is found that the effect is negligible even for the electron density 10(17) m(-3). (c) 2005 Elsevier B.V. All rights reserved.