This paper empirically tests for two competing explanations of the increasing sex ratio at birth (SRB) in India: prevalence of hepatitis B and human intervention in the form of sex selective abortion or female infanticide. First, I estimate a simple model of male-preferring stopping rule with data from three rounds of the National Family Health Survey in India (1992, 1998 and 2005) and find that the probability of a male birth varies significantly across birth parities. Second, I follow the epidemiological literature and use scheduled tribes as a novel proxy for the prevalence of hepatitis B in India, estimating the direct effect of hepatitis B on the SRB. Third, I estimate a full empirical model by endogenizing the probability of male birth with the hepatitis proxy as one of its determinants. In both cases, I find that hepatitis B has no impact on the probability of male birth. I conclude that human intervention in the form of sex-selective abortion or female infanticide, rather than biological factors like hepatitis B, explain the increasing SRB in India.