The restriction endonuclease BliAI, an isoschizomer of ClaI, which recognizes the sequence 5´-AT↓CGAT -3´, was purified from a natural isolate identified as Bacillus licheniformis. The restriction endonuclease was isolated from cell extracts using single-step purification by phosphocellulose column chromatography. The restriction endonuclease is active at 37ºC and over a wide range of pH and salt concentration. The molecular weight of the purified restriction enzyme is consistent with a value of 39 kDa.