Specific somatostatin receptors (ssts) have been described in normal and tumor tissues and identified on more than 95% of normal mitogen-activated human peripheral lymphocytes. Somatostatin may modulate the immune response by a variety of mechanisms, most of which are inhibitory, sst scintigraphy in patients with immune-mediated diseases revealed sst expression in 97% of patients with sarcoidosis, 100% of patients with tuberculosis or Wegener's granulomatosis, 75% of patients with Sjõgren's syndrome, and 50% of patients with systemic lupus erythematosus or uveitis. sst expression appeared to be related to progression or remission of disease. Patients who responded poorly to therapy remained positive at scintigraphy. Investigation of 10 human B-cell lines and eight human T-cell lines, using a polymerase chain reaction, revealed the presence of sst2-mRNA in two of the B-cell and two of the T-cell lines. Visualization of ssts on activated mononuclear leukocytes by sst scintigraphy may prove useful in evaluating the spread of immune-mediated diseases and their responses to therapy. The efficacy of octreotide should be studied in patients with these diseases.