In this study, delta-aminolevulinic acid dehydratase (ALAD) from Streptomyces yokosukanensis ATCC 25520, producer of an unusual purine riboside antibiotic called nebularine, was purified and characterized. Purification procedures were involved with ammonium sulphate precipitation and gel filtration techniques by use of Sephacryl S-200. After gel filtration a 90.76-fold purification was obtained. The maximum enzymic activity was observed in the supernatant after 100% precipitation. According to the data obtained from the investigation, the enzyme was found to be a single polypeptide having a molecular mass around 34.8 kDa. This was determined by SDS-PAGE. Its optimal temperature was around 45 degrees C, and optimal pH was found to be 8.0. Some heavy metals, Pb2+, Zn2+, Fe3+, Co2+, Mn2+, and Mg2+, inhibited its activity between 20-51%, and Ni2+ increased its activity up to 15%. The text was submitted by the authors in English.