The effects of Ambilhar (niridazole or nitrothiazole) on the calcium, magnesium and phosphorus contents of various tissues of rabbits were studied. It results in a decrease in the calcium content of bones, liver and muscles. A similar depletion of the magnesium content of brain, blood, liver and muscles was observed. On the other hand, the urinary excretion of calcium and magnesium was increased. These facts indicate that the drug possibly chelates with these divalent cations. This is supported by the ultra violet spectra of the complexes prepared in vitro.