In this study, we evaluated the frequency of formation of new lesions on brain magnetic resonance imaging (MRI) from patients with relapsing-remitting multiple sclerosis (MS) and defined the relative contributions of unenhanced and enhanced MRI. Every 4 weeks for 3 months, dual-echo and postcontrast T1-weighted (5 min after the injection of 0.3 mmol/kg gadolinium-DTPA) scans were obtained from 28 patients with relapsing-remitting MS. New lesions were defined as those present on dual-echo and/or postcontrast T1-weighted scans but with no corresponding MRI abnormalities on any of the preceding scans. A total of 111 newly formed lesions were detected during the follow-up on dual-echo and postcontrast T1-weighted scans (i.e., an average of 1.3 lesions per patient per month). Ninety-eight (88%) of such lesions were seen on both dual-echo and postcontrast T1-weighted scans, whilst 13 (12%) were seen only with one of the two techniques: 9 only on dual-echo and 4 only on postcontrast scans. Five of the 98 new lesions seen by both techniques were seen by postcontrast scans 1 month before their appearance on dual-echo scans. Our study suggests that both dual-echo and postcontrast T1-weighted scans are useful to detect newly formed lesions in patients with MS. This is of importance when using MRI to monitor the efficacy of treatments which may halt MS lesion formation.