A simple and reproducible typing system based on restriction fragment size of chromosomal DNA was developed to compare isolates of Streptococcus uberis obtained from the bovine mammary gland. The endonuclease giving the most useful restriction patterns was Hind III. Although seven other endonucleases (Bgl 1, Eco R1, Not 1, Pst 1, Sfi 1, Sma 1, Xba 1) were also tested in the system. An image analyser was used to obtain a densitometric scan and a graphic display of the restriction patterns. Such a system will allow large scale data storage for future computer-aided comparison.