Environmental challenges offer a potential method for predicting hypertension. They could be nutritional (eg, an increased salt load), behavioral (eg, a mental arithmetic task), or physical (eg, an exercise test) in nature. An ideal challenge test should be simple to administer, easily standardized, and with a response that can be precisely quantified. The response is best expressed as a change score from the baseline level, and should be reproducible over time. For the prediction of hypertension, blood pressure is the usual response measure, although others, such as heart rate, are possible. The response should have predictive value independently of other known predictors, including the baseline level. The dependent variables might be future blood pressure, target organ damage, or morbid events.