Sixty unselected consecutive patients with systemic lupus erythematosus (SLE) were prospectively evaluated for evidence of Sjögren's syndrome. This was diagnosed in the patients whose minor labial salivary gland biopsy was graded greater than or equal to 3 (according to Chisolm and Mason), who also had keratoconjunctivitis sicca (positive rose bengal eye test) and/or xerostomia (subjective xerostomia and decreased stimulated parotid flow rate). Lip biopsy revealed focal round cell infiltration compatible with a greater than or equal to 3 grade in 11 patients, minimal perivascular infiltration in 21 patients and no infiltration in 28. In the positive biopsy group (greater than or equal to 3 grade) subjective xerophthalmia, decreased parotid flow rate, parotid gland enlargement, lymphadenopathy, presence of rheumatoid factor and anti-La (SSB) antibodies were significantly commoner than in the others. Of the 11 patients of this group, 5 had keratoconjunctivitis sicca which sufficed for the diagnosis of Sjögren's syndrome, suggesting a prevalence of 8.3% in our population with SLE. In these individuals subjective xerophthalmia (40%), positive Schirmer's I eye test (60%), decreased parotid flow rate (80%), parotid gland enlargement (80%) and presence of rheumatoid factor (80%) and anti-La (SSB) antibodies (80%) were significantly more frequent than in the remaining patients, whereas significant differences regarding other features of SLE were not observed. Our results suggest that Sjögren's syndrome in SLE is relatively rare and usually mild. Furthermore, it may present more similarities to primary Sjögren's syndrome than to secondary Sjögren's syndrome accompanying rheumatoid arthritis.