Various strains of Escherichia coli, isolated from different patients, were screened for type II restriction endonuclease activity. In 1 out of 23 patients, a type II restriction endonuclease activity was found. The restriction endonuclease designated Eco1524I was purified to near homogeneity, based on hydroxyapatite and heparin sepharose chromatography. Eco1524I exhibited endonuclease restriction activity in the pH range from 6.0 to 10.0 (maximum level at pH 8.0) and required Mg2+ as divalent cation. The enzyme was stable till temperature 55 degrees C and pH range from 6.0 to 10.0. Eco1524I recognized the sequence 6-bp palindromic 5'AGG down arrow CCT 3', producing blunt end and is found to be an isoschizomer of Stu 1.