We evaluated the clinical usefulness of Tc-99(m)-N,N-ethylenedicysteine (Tc-99(m)-EC), a new renal tubular agent, in normal children and in children with various renal disorders and compared it with Tc-99(m)-mercaptoacetyltriglycine (Tc-99(m)-MAG3). In a first group of children (Group 1), which included 15 patients and 4 normal children, both Tc-99(m)-EC and Tc-99(m)-MAG3 renal scintigraphy were performed within a period of 1-5 days. In a second group (Group 2), consisting of 12 patients, only Tc-99(m)-EC scintigraphy was performed. In the normal children, renograms, differential renal function (DRF) ratios and semi-quantitative parameters of the two agents were similar. For Tc-99(m)-EC and Tc-99(m)-MAG3, the mean (+/- s.D.) time to peak activity (T-max) values were 3.2 +/- 0.5 and 3.1 +/- 0.4 min respectively, and the mean time from peak activity to 50% activity (T-1/2) values were 6.3 +/- 0.5 and 6.4 +/- 0.4 min respectively. The mean parenchymal transit time index (PTTI) and mean whole-kidney transit time index (WKTTI) for Tc-99(m)-EC were 1.7 +/- 0.3 and 2.8 +/- 0.4 respectively, and for Tc-99(m)-MAG3 they were 1.8 +/- 0.2 and 3.0 +/- 0.3 min respectively. There were also no significant differences between these parameters for the two agents in children with various renal disorders, and the correlation coefficients (r) for DRF, T-max, T-1/2, PTTI and WKTTI were 0.99, 0.98, 0.94, 0.77 and 0.63 respectively. We conclude that Tc-99(m)-EC has excellent imaging characteristics in children, and even has some advantages over Tc-99(m)-MAG3. We suggest this agent can be used routinely with children.