Glycosaminoglycan (GAG) production from cultured chondrocytes under different oxidative conditions. After the incubation times indicated, in the presence of 0.1 μmol/l H2O2 or 100.0 μmol/l ascorbic acid (initial subculture at the start of the experiment: 1 × 105 cells/dish, chondrocytes at passage 2), chondrocytes were collected and transferred to a new culture dish (1 × 105 cells/dish). Following 12 hours of incubation, the amount of GAG in the supernatant was measured using a spectrophotometric assay with dimethylmethylene blue. Values are expressed as the mean ± standard deviation of nine donors (n = 4 culture dishes per treatment group at each incubation period; *P < 0.05, **P < 0.01, versus control group at each incubation time). The H2O2 treated group exhibited a significant decrease in GAG production by chondrocytes as compared with the control group at all incubation times. In the antioxidative agent group the level of proteoglycan production tended to increase as compared with the control group, although no significant differences were observed between the control groups and antioxidative agent groups at any incubation time.