During the period of 1998 to 2004, surveys for dictyostelids (cellular slime molds) and myxomycetes (plasmodial slime molds or myxogastrids) were carried out at numerous study sites throughout the Great Smoky Mountains National Park as one component of the All Taxa Biodiversity Inventory (ATBI) project. As a result of these surveys, some general patterns have emerged relating to the occurrence and distribution of these two groups of organisms in the Park. Since the surveys began, the number of dictyostelids known from the Park has increased from 12 to at least 30, the highest total known for any comparable region outside of the tropics. Ten of the 30 species were described as new to science from material collected in the Park. Many of these are “small” species (<2 mm total height) that seem to be confined to marginal habitats at high elevations. The number of myxomycetes known from the Park has increased from 88 to approximately 220, but there are likely to be many additional records as the surveys continue. A number of myxomycetes appear to be restricted largely or exclusively to the Picea rubens (Red Spruce)—Abies fraseri (Fraser Fir) forests found at the very highest elevations in the Park. These forests are currently under considerable environmental stress as the result of industrial pollution and possible global climate change.