Flow cytometry of Group 1 individuals (at 3.75 yrs post-op, last follow-up) PBMC’s after 48 hrs of challenge with Co, Cr, and Ni (0.1mM) at 1×106 cells per 96-well conducted in triplicate for each individual and analyzed for CD4+ and CD8+ T-cell activation using CD25+ and CD69+ activation markers. (a) 8 of 17 metal-reactive Group 1 participants determined by LTT (SI>2) demonstrated significantly increased CD4+CD25+ over the average of 9 of 17 non-reactive individuals (p=0.05). (b) On an individual metal basis, Group 1 metal-reactive individuals were more CD25+ compared to non-reactive subjects for Cr and Ni. (c) Supernatants of these challenged PBMCs were analyzed for 10 cytokines; only IL-1b, IL-12 and IL-6 were significantly elevated in LTT reactive vs. non-reactive individuals (p<0.1).