Obesity, a state that may be characterized by a low-grade inflammation, has been associated with asthma. C-reactive protein, an acute phase reactant, is elevated in obese people. However, little is known about how asthma affects C-reactive protein concentrations. Using data from 14,224 participants of the Third National Health and Nutrition Examination Survey (1988-1994), the author examined C-reactive protein concentrations among participants with current asthma (n = 651), who formerly had asthma (n = 303), and who never had asthma (n = 13,270). Compared with 21% of participants with current asthma, 11% with former asthma (P < .001) and 15% without asthma (P = .018) had C-reactive protein concentrations > or = 85th percentile of the sex-specific distribution. Compared with participants without asthma, the age-adjusted odds ratios for having an elevated C-reactive protein concentration was 1.49 (95% confidence interval [CI]: 1.11, 2.00) for persons with current asthma. After adjusting for age, sex, race or ethnicity, years of education, cotinine concentration, body mass index, waist-hip ratio, physical activity level, aspirin use, oral corticosteroid use, and inhaled corticosteroid use, the odds ratio decreased to 1.15 (95% CI: 0.83, 1.59). Body mass index was the main reason for the attenuation of the odds ratio. Whether the inflammatory activity associated with body mass index contributes to the pathophysiology of asthma is unknown.