Risk is a function of toxicity and exposure. Regulatory agencies assess the risks associated with pesticide usage, and act to mitigate workers' and the public's exposures to acceptable levels. The regulatory actions assume that there is a high degree of certitude associated with the values calculated by the risk assessment process. In truth, the degree of uncertainty may be very great. Sources that contribute to the uncertainty of the numbers vary, and the magnitude of the imprecision varies as well. The ambiguities contained in the risk assessments by two regulatory agencies concerning chlorpyrifos, molinate, thiabendazole, and phosphine are presented to gain insight by example. Despite the detailed uncertainties, risk assessments are still needed by regulatory agencies. Various interest groups and politicians try to use the uncertainties in a risk assessment to justify their positions. The appropriate place to take into account the views of disparate interest groups is in the risk management process. Risk assessments will be disputed from all sides, the logic employed should be carefully layed out, and the assessor should strive for as much accuracy as science permits.