A method to generate a pattern of DNA restriction fragments that is unique to an individual, especially for forensic purposes. DNA from blood, semen or another tissue sample is isolated and cleaved with a restriction endonuclease; the products are separated by polyacrylamide-gel electrophoresis, blotted on to a nylon sheet, and fragments that contain a specific nucleotide sequence are detected by hybridization with an appropriate DNA probe to produce the unique pattern.