(e, 2e) triple differential cross sections for the ionization of Ar (3p) by 70.8 eV electron impact are calculated in the coplanar asymmetric geometry using the modified distorted-wave Born approximation, and compared with the recent experimental data of Ren et al. Ren et al. 2012 Phys. Rev. A 85 032702. The results show that electron exchange effect and post-collision interaction play an important role in the (e, 2e) process of low-energy electron impact.