The fungus, Aspergillus niger, has been demonstrated to produce a growth substance active in the Avena test (4, 16). Boysen-Jensen (5) showed that the active material was soluble in ether under slightly acid conditions and that the fungus could convert tryptophan, lysine, leucine, tyrosine, histidine and phenylalanine into growth substance. The work of K?gl and Kostermans (12) established further that the molecular weight of the growth regulator was 169, a value which closely approximates that expected for indoleacetic acid (IAA). These lines of evidence suggest that IAA is produced by A. niger. IAA has been clearly shown to be the growth substance in the culture filtrate of Rhizopus suinus (18). As a part of a routine screening program, seeking to detect fungus products that influence the growth of higher plants, it was recently discovered that culture filtrates of a fungus isolated from soil induced in plants effects which somewhat resemble those caused by known growth substances. However, the effects are distinctly different from those caused by IAA and evidence will be presented which eliminate IAA as the causative agent. Other preliminary studies concerning the active compound will also be reported in the present paper. The fungus responsible for these effects is designated as 56-39 and has been identified as A. niger.