The following conclusions are drawn from the results of the study: Extreme care must be exercised in the preparation of chemically defined media if precipitation of trace metals is to be prevented. The only trace metal required for growth of the fungus, Fusarium, on acetate, glucose and glycerol media was iron. Zinc was a stimulant for Fusarium growth on acetate and glucose, but was not required for moderate growth. The only trace metal required for growth of the fungus, Geotrichum on glucose and glycerol media was zinc. This organism required only iron for growth on acetate medium. Iron was a stimulant for Geotrichum growth on glucose and glycerol, but was not required for moderate growth. Glucose media containing only the trace metals iron and manganese yielded the optimum growth characteristics for the mixed culture studies. Acetate media containing only the trace metals iron or manganese yielded the optimum growth characteristics for the mixed culture studies.