Technical Abstract: Tree nuts, while not generally regarded as a staple food, are particularly appreciated by consumers for their flavor and convenience. Most consumers regard nuts as "natural" foods and have little concern for adverse or deleterious effects other than occasional allergenicity in some individuals. Development of off-flavors from rancidity and infection with spoilage microorganisms (generally Aspergillus niger, Penicillium spp., and Rhizopus spp.) are so obvious that such nuts are usually discarded and not eaten. Nuts contain high levels of protein, fiber, and dietary fats, which in association with their pleasant flavor and convenience, has led to the recommendation that they should be an essential part of a healthy diet. Tree nuts are an extremely valuable agricultural commodity in national and international trade. A serious constraint on the marketing of tree nuts, is the potential presence of aflatoxins, which are highly regulated because of food safety concerns. In 2005, 94% of the rapid alerts or notifications from the EC Rapid Alert System for Food and Feed (RASFF) for mycotoxins in tree nuts were for aflatoxins, with 28 for almonds and 13 for pistachios from the U.S. While this is a small number relative to the total of 827 alerts for all mycotoxins in tree nuts, it represents considerable economic loss to California producers and exporters, due to lost revenue, return or reprocessing of the shipment and increased sampling of subsequent imports.