We performed 15 dynamic gadolinium-DTPA (Gd-DTPA)-enhanced MRI studies in 8 patients with relapsing and remitting multiple sclerosis; 7 were follow-up studies. We measured the time course of enhancement in 102 enhancing lesions for up to 384 minutes, with rest breaks. Immediate postcontrast MRIs demonstrated many different patterns of enhancement. We observed both uniformly enhancing and ring enhancing lesions. The enhancing regions were often less extensive than the corresponding high signal on T2-weighted images. Three lesions were seen with Gd-DTPA but not on unenhanced scans; 1 was seen on unenhanced scans 10 days later, suggesting that blood-brain barrier disturbance may precede other MRI signs of MS lesions. Three months later, some high-signal areas on T2-weighted scans had decreased in size to resemble the areas previously outlined by Gd-DTPA. This technique provides useful information about the pathogenesis and behavior of MS lesions.