Confluent, primary cultures of rPT cells were incubated with the indicated concentrations of HgCl2 for 24 h. Activities of γ-glutamylcysteine synthetase (GCS), glutathione peroxidase (GPX), glutathione S-transferase (GST), and glutathione disulfide reductase (GRD) were measured in cellular homogenates by spectrophotometric assays. Control activities (= 100%; in mU/mg protein) were 611 ± 93, 237 ± 8, 64.0 ± 3.4, and 2.40 ± 0.99 for GCS, GPX, GST, and GRD, respectively. Results are expressed as the percent of control ± SE for measurements from 3 separate cultures for each concentration of Hg2+. *Significantly different (P < 0.05) from the corresponding control sample.