Because interferon injections have recently been reported to induce cortisol in cancer patients, we retrospectively reviewed cortisol levels obtained during a preliminary trial of the interferon inducer polyriboinosinic polyribocytidylic acid in poly-L-lysine and carboxymethylcellulose (poly ICLC) in multiple sclerosis patients to determine if significant cortisol induction occurred. Analysis of data from 51 poly ICLC infusions in 6 men and 4 women showed elevated cortisol levels 4 to 16 hours after infusion, with hematological changes consistent with steroid effect. The highest cortisol levels observed were in 2 patients who improved during the treatment period, but there was no clear relationship between cortisol levels and clinical outcome in the group as a whole.