Method of treating autoimmune conditions are disclosed comprising administering to a mammalian subject IL-12 or an IL-12 antagonist. In certain preferred embodiments the autoimmune condition is one which is promoted by an increase in levels of IFN-.gamma. or TNF-.alpha.. Suitable conditions for treatment include multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, autoimmune pulmonary inflammation, Guillain-Barre syndrome, autoimmune thyroiditis, insulin dependent diabetes melitis and autoimmune inflammatory eye disease.