We appreciate the comments of Macleod and Davey Smith on our article reporting an association between systemic inflammation markers and socioeconomic status.^1,2 In their letter, Macleod and Davey Smith state that our findings, particularly the association of fibrinogen with socioeconomic status, and its interpretation is not correct, and runs contrary to the principle of “Mendelian randomisation”. As the evidence, they refer to the finding that plasma fibrinogen concentrations are related to a polymorphism in the β-fibrinogen gene, with presence of the “T” allele being associated with higher levels. According to the authors, this finding is in keeping with the evidence from controlled trials that suggests that drugs lowering fibrinogen do not decrease the …