This paper examines the effects of changes in labor market opportunities for women on the bargaining power of women within households and, ultimately, on investment in children’s human capital. I show that a positive demand shock for female labor in a woman’s age category increases her bargaining power, and this raises investment in the health of girls relative to that of boys within the household. To identify this effect, I exploit the geographic heterogeneity in demand for younger versus older female labor within the Mexican export manufacturing sector and its differential changes across municipalities between 2002 and 2005. I find that a 1 percent increase in labor demand for older (mostly married) women, caused by a demand shock to the export manufacturing sector, raises the share of decisions made by the wife in a household by 1.3 percent and the chance of a daughter being in good health by 1.1 percent.