The antibiotic drug 4,4'-diaminodiphenylsulphone (DDS) is used to treat several dermatologic diseases, including Hansen's disease. This study confirmed the antioxidant nature of DDS in hydrogen peroxide (H(2)O(2))-induced oxidative stress and assessed its role in other apoptotic stresses in human diploid fibroblasts (HDFs). Oxidative stress was effectively reduced by DDS in a dose-dependent manner. Moreover, the oxidative stress-induced increases in the levels of the p53 and p21 proteins were inhibited by pre-treatment with DDS. In addition, H(2)O(2) and DDS increased the level of cytochrome P450 (CYP450) IIE1 in HDFs, implicating a role for DDS in H(2)O(2) scavenging via the activation of CYP450. DDS treatment increased the activity of catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR), as well as the GSH/GSSG ratio, indicating activation of the glutathione system against oxidative stress. However, DDS showed no protective effects on HDFs against other apoptotic stimuli, such as thapsigargin and staurosporine, suggesting that DDS would act only against oxidative stress. Therefore, in addition to its antibiotic function, DDS is a potent antioxidant against H(2)O(2)-induced oxidative stress in HDFs.