SUMMARYThe occurrence and distribution of cellular slime molds were studied in relation to altitude of Southern Appalachian forest sites. Nineteen sites were sampled in seven forest types at elevations between 230 and 1,800 m. The diversity of cellular slime molds was greater than in other geographical areas of temperate North America. Twelve described dictyostelid slime molds and one acrasid slime mold were isolated in addition to a new species of the genusPolysphondylium, and a naturally occurring mutant of uncertain affinity. One species,Acytostelium subglobosum, was isolated for the first time in North America. Optimum forest habitats in terms of acrasian diversity were between 590 and 820 m. Segregation of species by altitude was similar to that by latitude, again indicating a strong climatic influence on distribution.