This study examined psychologic distress and immune function in patients with chronic-progressive multiple sclerosis participating in a placebo-control trial of cyclosporine. Immune measures included percentages and absolute numbers of CD2+, CD4+, CD8+, Leu-11-b+, HLA-DR (IA+), and transferrin-receptor-positive cells, which were evaluated by immunofluorescence using monoclonal antibodies. Distress was measured with self-report scales. The Expanded Disability Status Scale assessed neurologic disability. Subjects were followed up for 2 years, and their high-depressed and low-depressed times were compared. Times of greater depression were associated with lower CD8+ cell numbers and CD8+%, and a higher CD4/CD8 ratio. CD4+ cell numbers and percent were also higher when subjects were depressed, but only in the placebo group. There were no differences in Expanded Disability Status Scale when subjects were more depressed. Evaluation of a single subject revealed that Ia+ and transferrin-receptor-positive lymphocytes increased 3 months before distress increased. It was concluded that distress is associated with immune dysregulation in multiple sclerosis, although the mechanisms of this association have yet to be delineated.