We studied concentrations of C-reactive proteins (CRP) in a population-based sample of 3204 men aged 45-74 years. Obesity was identified in 726 (23%) men (body mass index (BMI) >30 kg/m(2)). Stratification of the sample into three levels of depressive mood revealed a significant association between increased CRP in the obese sample with highest level of depression in comparison to the low level obese depression group (p=.013). The obesity x depression interaction was significant (p=.021). Multivariate analysis confirmed this effect after adjusting for possible confounding variables (age, high blood pressure, smoking, physical inactivity, low social class, and low alcohol intake) (p=.008). In the non-obese sample, there was no association between depressive mood and concentrations of CRP. These findings suggest a possible synergistic effect of obesity and depressive mood on chronic low level inflammation which may play a crucial role in the pathogenesis of atherosclerosis.