With a few important exceptions, most pesticides have low volatility. However, a significant number of the industrial chemicals under the jurisdiction of TSCA have sufficient volatility to affect availability in fortified test diets and consequently the test results. Although extremely volatile chemicals might evaportate from test diets, there is insufficient data to indicate what levels of volatility are of concern. Volatility may be only one of a variety of factors influencing the fate of organic chemicals in test diets. Other mechanisms such as hydrolysis, adsorption, and photolysis should also be considered, but for many chemicals having significant vapor pressures, volatility is likely to be the major source of loss.