To assess the usefulness of the 99Tcm-N,N'-ethylene-1-dicysteine (99Tcm-EC) complex for examination of kidney function, dynamic kidney scintigraphy with 99Tcm-EC and clearance determinations were performed. During renoscintigraphy the kidney images were of superb quality, with overlying organs (liver, spleen) not visualized. Renograms showed typical shapes, their Tmax and T1/2 values being unsignificantly different from the values obtained with other radiopharmaceuticals used in renoscintigraphy (mercaptoacetyl triglycine, hippuran). Very strict correlations were found between values of 99Tcm-EC and 131I-iodohippurate (OIH) clearances (r = 0.91) and excretion rate constants (r = 0.92) for both radiopharmaceuticals. The correlation enabled the formulation of an equation by which effective renal plasma flow (ERPF) could be established from 99Tcm-EC clearance: ERPFOIH = 1.245 x ClEC + 51.52. On the basis of this equation a lower boundary of the normal 99Tcm-EC clearance was established; it amounts to 300 ml min-1 1.73 m-2.