Adults aged 55 years or older with both MS and MCI at baseline will be randomized to a 6-month intervention with either (1) treatment with pioglitazone, (2) endurance exercise training, or (3) control (placebo and no exercise). The hypothesis is that treatment with the TZD pioglitazone or EET will improve cognitive function compared to controls, as evidenced by either improvement, stabilization, or lesser decline in performance on cognitive testing. Participants will undergo a physical exam including blood and urine tests, a complete neurologic exam, and a comprehensive battery of cognitive tests. They will also have a DEXA scan, exercise treadmill test, non-invasive tests of vascular function and a hyperglycemic-euglycemic clamp procedure to measure insulin resistance.