['To investigate the link between serum vaspin levels and physical activity and/or physical fitness in Japanese.', 'A total of 156 subjects (81 men and 75 women) was enrolled in this cross-sectional study. Serum vaspin levels, physical activity by uniaxial accelerometers, peak oxygen uptake, and metabolic risk parameters were evaluated. We also assessed anthropometric and body composition parameters.', 'Serum vaspin levels were over the level of 10\xa0ng/mL in 15 subjects (9.6\xa0%: Vaspin High group). In Vaspin Low group (<5\xa0ng/mL: 74 men and 67 women), serum vaspin levels were 0.12\xa0±\xa00.18\xa0ng/mL in men and 0.39\xa0±\xa00.70\xa0ng/mL in women. Peak oxygen uptake was significantly and positively correlated with serum vaspin levels even after adjusting for age, physical activity evaluated by Σ[metabolic equivalents\xa0×\xa0h per week (METs[Symbol: see text]h/w)], BMI, and other confounding factors in men. In turn, physical activity was significantly and positively correlated with serum vaspin levels even after adjusting for confounding factors in women.'] Are serum vaspin levels associated with physical activity or physical fitness in Japanese : a pilot study?