Biological information is frequently collected to evaluate our health. We take our temperature to determine whether we have a fever (and whether it’s going up or down); we measure lead levels in blood to screen for toxic exposures that require prompt treatment (and to evaluate the effectiveness of that treatment); we measure red blood cell levels to screen for anemia (and to confirm its successful resolution); and we measure blood pressure and cholesterol levels to identify treatable risk factors for cardiovascular disease before they become symptomatic. With advances in science and technologies, we now have new and emerging opportunities to use biological information wisely to assess how adverse experiences and preventive interventions are affecting the foundations of health and development in young children before serious problems arise.