[en] Certain ^99mTc-labeled derivatives of ethylene diamine substituted in NN', when labeled with ^99mTc, have been proposed for studying renal excretion, and others for brain imaging. Ethambutol, a well known antituberculosis drug, possesses a structure very similar to these derivatives. We prepared a complex of [^99mTc]ethambutol using hypophosphorus acid as the reducing agent. The complex was then analyzed by paper and cellulose F chromatography and by FAB mass spectrometry. A pharmacokinetic study in the mouse and rat indicated that the complex is eliminated by the kidney faster than DTPA, slower than [¹³¹I]hippuran and without significant renal retention. The [^99mTc]ethambutol complex is easy to prepare and shows good stability in water at physiological pH, making it potentially useful in renal excretion studies. (author)