The newly developed 99mTc-labeled renal imaging agent, mercaptoacetyltriglycine (MAG3), is a tubular secreted compound. It is expected the most suitable agent to measure renal function and image urinary tract because of the excellent imaging properties and availability of 99mTc and preferred biological qualities of radiohippurates. We examined 15 patients (8 males, 7 females, mean age 55 years old) with renal and urinary tract disease. After drinking 400 ml of water, 185, 370 or 555 MBq of 99mTc-MAG3 was injected with the supine position. Dynamic scans were acquired for 20 minutes on a large field of view gamma camera (ZLC-7500 Siemens Medical Inc.) linked to a computer system (Scintipac-2400 Shimadzu Co.) in a 64 x 64 matrix. Regions of interest (ROI) were placed around each kidney. Curves of 12 seconds frame rate were generated from all two ROIs over the 20 minutes study. The time to peak count (Tmax) and time from peak count to a half count (T1/2) were calculated from the curve data. 99mTc-DTPA renal imaging was examined to the same patients with the same method like 99mTc-MAG3. The renogram of 131I-orthoiodohippurate (OIH) was performed with probe method. The excellent quality of the renal image was obtained with 185-555 MBq of 99mTc-MAG3 compared with the same dose of 99mTc-DTPA respectively. The diagnostic value of 99mTc-MAG3 renal imaging was as well as 99mTc-DMSA renal imaging. The Tmax of 99mTc-MAG3 renogram was same value of that of both 99mTc-DTPA and 131I-OIH renogram. The T1/2 of 99mTc-MAG3 renogram was significantly lower than that of 99mTc-DTPA renogram. The T1/2 of 99mTc-MAG3 renogram was slightly higher that of 131I-OIH renogram. We conclude that the renal imaging of 99mTc-MAG3 was able to acquire the most excellent image and the proper renogram pattern as same as 131I-OIH renogram.