Chondrocytes are the only cells in articular cartilage and are responsible for extracellular matrix metabolism, which confers its characteristic ability to withstand compression and distribute load (1). Osteoarthritis is characterized by an abnormal matrix metabolism which leads to a dysfunction of articular cartilage; this disease is associated with obesity, associated to an increase in leptin, TNF alpha, IL-1 and insulin. Chondrocyte intracellular calcium concentration (ICC) and pH (IpH) regulate matrix metabolism (2). In the present study, the effects of these substances on ICC and IpH, in human articular chondrocytes freshly isolated from healthy and osteoarthritic cartilage, were determined. Cells were isolated from knee or hip load-bearing car-tilage that was obtained from patients undergoing orthopedic surgery. All patients signed an informed consent form. Cells were isolated using a standard method (3). ICC and IpH were measured by fluorescence employing Fura-2 and BCECF-loaded cells respectively, previous a standard calibration for each dye. The measurements were made in human chondrocytes from healthy cartilage (HCHC) and osteoarthritic cartilage (HCOC). Initial ICC was 88±14 nM in HCHC (n=38) and 79±12 nM in HCOC (n=36), with no significant differences between them. In HCHC, insulin, TNF alpha and IL-1 increased significantly ICC immediately after the application of each agent to 382±34 nM (n=12), 551±32 nM (n=8) and 604±44 nM (n=8) respectively (p<0.05 in all cases when compared with control); there were also significant differences between ICC increase induced by TNF alpha and IL-1 when compared with the ICC increase induced by insulin. In HCOC the effects of insulin, TNF alpha and IL-1 on ICC were in the same trend, but they were significantly lower: 211±21 nM (n=9), 243±32 nM (n=9) and 216±24 nM (n=8) respectively, without any significant differences. In both cells, leptin had no significant effect on ICC: 84±21 nM in HCHC (n=10) and 70±26 nM in HCOC (n=10). On the other hand, initial IpH was 6.94±0.21 in HCHC (n=26) and 6.32±0.12 in HCOC (n=26), with a significant difference between these two data (p<0.05); only IL-1 was able to decrease IpH to 6.21±0.16 (n=8) and 6.02±0.09 (n=8) respectively; in both cases the differences were significant (p<0.05). Insulin, TNF alpha and leptin had no effect in both groups of cells. In summary, these findings may help to understand the association between obesity and osteoarthritis because leptin, TNF alpha, IL-1 and insulin are all increased in obesity as a consequence of a metabolic misbalance; the effects of them on chondrocyte calcium and pH homeostasis can affect matrix metabolism and hence cartilage function, which can lead to osteoarthritis.