Pixel-by-pixel calculation of T1 values (T1 mapping) has been used in different tissues to focus on T1 changes in a quantitative fashion. The aim of this study was to establish T1 mapping of human myocardium on a 1.5 Tesla system and to examine its diagnostic potential in patients with acute myocardial infarction (AMI). 8 patients with reperfused AMI (day 3 +/- 1) underwent multi-breath-hold MRI in a 1.5 Tesla system. Sets of five images with varying T1 weighting were acquired prior to and after the administration of contrast agent to generate images from calculated T1 values (T1 mapping). Prior to the contrast agent administration, all patients showed T1 prolongation in the area of infarction, which was identified in separate measurements using the delayed enhancement approach. Compared to noninfarcted areas, T1 values in the infarcted areas were increased by 18 +/- 7% (SE, p < 0.05). The spatial extent of the area of T1 prolongation was larger than that of the hyper-enhanced areas in conventional contrast-enhanced images. T1 maps obtained after the application of Gadolinium-DTPA revealed a T1 reduction of 27 +/- 4% in infarcted tissue compared to noninfarcted areas (p < 0.05). The areas showing T1 reduction were in agreement with the hyper-enhanced regions in conventional T1-weighted images. T1 mapping visualizes changes in the longitudinal relaxation time induced by AMI. T1 mapping can detect myocardial necrosis without the use of contrast media. Information that can be extracted from a combination of pre- and postcontrast T1 maps exceeds that from conventional contrast studies.