One hundred and sixty-four clinical isolates of Pasteurella multocida recovered from two swine herds in Minnesota were characterized by restriction endonuclease analysis (REA) and rRNA gene restriction fragment length patterns. Bacterial DNA was digested with HpaII and electrophoresed in 0.55% agarose. Restriction fragments were transferred by Southern blot to nylon membranes and then hybridized with digoxigenin-dUTP-labeled Escherichia coli rRNA. Four different REA patterns were observed among the 156 serotype A strains isolated from herds A and B. The two most common REA types (1 and 2) represented 92% of the strains analyzed, while REA types 3 and 4 were observed only in lung samples and accounted for 8% of the isolates. Two different ribotypes were observed for these serotype A isolates. Ribotype I consisted of the most common types, 1 and 2, found by DNA fingerprinting. Ribotype II included REA types 3 and 4. Results from both herds suggest that in closed swine populations, a single strain of P. multocida predominates and causes disease. It is concluded that these genomic fingerprinting techniques were highly discriminatory and that capsular serotyping in combination with REA or ribotyping is an appropriate technique for epidemiological studies of P. multocida of swine origin.