MRL/lpr mice are studied as one of the animal models of the human autoimmune disease Sjögren's syndrome. The mice develop inflammatory exocrinopathy resembling that of patients with Sjögren's syndrome. To investigate if MRL/lpr mice produce the anti-Ro/SS-A and anti-La/SS-B autoantibodies common to Sjögren's syndrome patients, mouse sera were tested in ELISA and Western blot with recombinant Ro 60,000 MW, Ro 52,000 MW and La antigen. Thirty per cent of mice aged 4 months and 5% of mice aged 2 months produced antibodies to human Ro 52,000 MW. Antibodies to Ro 60,000 MW and La were found in a low percentage of the older mice but not at all in the younger mice. Immunohistological staining of mouse organ sections demonstrated anti-Ro 52,000 MW-producing cells in spleen, lymph nodes and salivary glands of seropositive animals. These findings provide further evidence for the usefulness of the MRL/lpr mouse as a model for Sjögren's syndrome.