Microorganisms utilizing erythhro-Ls-isocitrate (L-alloisocitrate) were isolated from soil after enrichment culture in medium containing the acid as the sole carbon source. Most isolates were bacteria, and NAD+-linked L-alloisocitrate dehydrogenase activity was found in some of their cell-free extracts. A bacterial strain No. 2 showing the highest enzyme activity was identified as belonging to genus Pseudomonas. A fungal strain showing good growth on L-alloisocitrate but restricted growth on glucose was also isolated and identified as belonging to genus Acremonium. No dehydrogenase nor oxidase activity was detected for L-alloisocitrate in extracts of the fungus, although conversion of the acid to fumarate was suggested in tracer experiments with intact cells.