In the course of screening for herbicidal substances from antimetabolites produced by microorganisms, we have isolated a metabolite of Streptomyces sp. OH-5093 which inhibits the growth of radish and sorghum. The structure was established to be 4-chlorothreonine (1). We also found that 4-chlorothreonine is an amino acid antimetabolite with anti-Candida activity. 4-Chlorothreonine is a constituent of the naturally occurring syringostatins1)2) and syringomycin3'4) and is a product of synthesis5'6) and enzymatic conversion7). However, no papers have reported the occurrence of 4 chlorothreonine as a microbial metabolite nor its herbicidal properties. This note describes the fermentation, isolation, structure identification and biological activities of 4-chlorothreonine.