Ten patients with relapsing-remitting multiple sclerosis have been studied by serial gadolinium-pentetic acid magnetic resonance imaging (MRI) every 14 days for 3 months. At the end of the follow-up, seven relapses occurred in six patients; no therapy was administered during the study. Ninety-three enhancing lesions were collected in eight patients. With regard to the duration of the enhancement, 32 lesions were detected in only one MRI scan and 32 were found in more MRI scans (most of the lesions occurring in two serial examinations). Four old lesions increased their size with delayed enhancement. Correlation was found between the relapses and the gadolinium-pentetic acid-enhancing areas only for one brain-stem and two cervical spinal cord lesions. Gadolinium-pentetic acid MRI provides useful information about activity of the disease that cannot be obtained clinically even if the dynamic of the lesions may be undervalued in old plaques.