We measured halogenated organic contaminants (HOCs) [polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and dichloro-diphenyl-trichloroethane (DDT)] and P450 [e.g., ethoxyresorufin-O-dealkylase (EROD)] stress in livers from Caspian tern (Hydroprogne caspia) adults and Forster’s tern (Sterna forsteri) adults and chicks in San Francisco Bay (SFB). Penta BDEs and tetra PBDEs composed 46–66% of ∑PBDE in terns. PCB homologues di, tri, penta, hexa, and hepta composed 93–95% of ∑PCBs and p′p-DDE composed 82–98% of all ∑DDTs. We found similar concentrations of ∑PBDEs [mean micrograms per gram wet weight (ww) ± standard error = 0.4 ± 0.1], ∑PCBs (5.9 ± 1.6), and ∑DDTs (0.6 ± 0.1) among species, sexes, and regions. However, concentrations were higher in Forster’s tern adults than chicks (∑PBDEs = 0.4 ± 0.1 and 0.1 ± 0.1; ∑PCBs = 7.08 ± 2.4 and 2.4 ± 1.4; ∑DDTs = 0.5 ± 0.1 and 0.1 ± 0.1; respectively), and there was a nonsignificant trend of elevated ∑PBDEs and ∑PCBs for adult Forster’s terns in the Central South Bay and Lower South Bay portions of SFB. Combined Forster’s tern and Caspian tern ∑DDTs bioaccumulated similarly to selenium, but not mercury, and there was a nonsignificant but positive trend for ∑PBDEs and ∑PCBs bioaccumulation with mercury. P450 protein activity was higher in adult Forster’s terns than Caspian terns, higher in Central South Bay than in Lower South Bay, and higher in adult Forster’s terns than in chicks.