123I-metaiodobenzylguanidine (MIBG) myocardial scintigraphy was performed in twelve normal human subjects, and the distribution and clearance of MIBG were estimated. In PLANAR studies, heart to mediastinum (H/M) and lung to mediastinum activity ratio (L/M) were 2.68 +/- 0.45 and 1.82 +/- 0.23 in initial images, and 2.75 +/- 0.44 and 1.55 +/- 0.13 in delayed images. The clearance of MIBG in the lung was more rapid than that in the heart, 41.6 +/- 4.1 vs. 29.8 +/- 3.2 (%), therefore MIBG cardiac profiles were more clarified in delayed images. In SPECT studies, the regional relative uptake (RRU) in anterior, septal, inferior and lateral wall were 100.0 +/- 0, 93.9 +/- 6.9, 85.0 +/- 10.0 and 104.9 +/- 8.3 (%) in initial images, and 100.0 +/- 0, 96.8 +/- 9.6, 79.4 +/- 8.3 and 99.1 +/- 7.9 (%) in delayed images, respectively. The RRU in inferior wall was significantly lower than those in the other walls. The regional clearance rate (RCR) in these four walls were 25.1 +/- 4.6, 22.5 +/- 8.2, 29.7 +/- 8.3, 29.3 +/- 3.4 (%), respectively. The RCR in inferior and lateral wall were significantly larger than those in anterior and septal walls. The RRU in basal, mid and apical portion were 100.0 +/- 0, 104.5 +/- 3.3, 98.9 +/- 12.1 (%) in initial images, and 100.0 +/- 0, 103.9 +/- 4.5, 96.8 +/- 15.2 (%) in delayed images, respectively. The RRU in mid portion was significantly higher than that in basal portion.(ABSTRACT TRUNCATED AT 250 WORDS)