A new streptomycete metabolite named arglecin was isolated from the culture filtrates of the strains KA57-AG3, KB59-M1 and the other ll strains by the screening of compounds with positive Wood and diacetyl reactions. The structure was determined as 5-amino-2-(3-guanidinopropyl)-3,4-dihydro-4-isopropylpyridin-3-one.As the results of our screening of culture filtrates of microorganisms for chemical color reactions, clienomycins2) and sphydrofuran3) have already been found as new metabolites of streptomycetes. This screening method appears to be useful in finding the significant metabolites which may reveal biosynthetic sequences in microorganisms. This paper describes the isolation and the chemical structure of a new metabolite named arglecin which was found by the screening of compounds of positive Wood4> and diacetyl reactions.