Reactions of 3-substituted-5-(2-aryl-2-oxoethylidene)-2-thioxothiazolidin-4-ones 2a, b with 2.5 equiv. of hydrazine hydrate were carried out with reflux and/or at room temperature. Both of these conditions gave 4-(3-aryl-4,5-dihydro-1H-pyrazole-5-carbonyl)-4-(2-methoxyphenyl)thiosemicarbazides 3a, b and4-(2-methoxyphenyl) thiosemicarbazide 4. Inaddition, the 6-(2-oxo-2-phenylethyl)-4-(2-methoxyphenyl)-3-thioxo-1,2,4-triazinan-5-one 5a was obtained from 2a.The successful isolation of sulfur from these reactions was the key to rationalize the above mentioned transformations. The structures of all the products were evidenced by microanalytical and spectral data.