This study considers the eradication of hookworm disease from the American South as a test of the quantity-quality (Q-Q) framework of fertility. Eradication was principally a shock to the price of quality because of three factors: hookworm (i) depresses the return to human-capital investment, (ii) had a very low case-fatality rate, and (iii) had negligible prevalence among adults. Consistent with the Q-Q model, we find a significant decline in fertility associated with eradication. Relative sizes of fertility and human-capital responses to hookworm indicate that the Q-Q mechanism is of a similar magnitude to secular co-movements in these same variables.