Haptoglobin (Hp) levels were measured in blood serum from 185 apparently healthy ringed seals (Pusa hispida) from Svalbard (age range, 1–30 yr) collected during the spring seasons of 2002 through 2004. The Hp concentration was 0.26±0.02 g/l (mean±SE; range, 0.0–1.5 g/l). Maturity status, body condition index (CI), interactions between CI and maturity status, and sex and maturity status all had significant influences on Hp levels. Mature males had significantly higher Hp concentrations compared with mature females (0.30±0.03 vs. 0.17±0.01 g/l, F_1,16=14.9, P<0.01). No differences were found between Hp levels in immature male and female seals (0.33±0.06 g/l). The Hp levels increased significantly in immature seals when the CI decreased. Despite the fact that mature males had a significantly lower CI than mature females, no direct correlation was found between Hp concentration and CI among adults. The elevated Hp values found in mature males might be related to injuries inflicted among males while fighting during the mating season or to high stress levels related to mating competition. The Hp concentrations of ringed seals measured in this study are useful baseline data for development of a diagnostic tool for future monitoring of the general health of this and other ringed seal populations.