The reactions of 3-methyl-1-phenyl-5-oxo-${Delta}^2$-pyrazoline-4-thiocarbohydrazide towards phenyl isothiocyanate, sodium nitrite, cyclohexanone, aromatic aldehydes, and carbon disulphide has been studied. The Vilsmeier-Haack reaction has been applied on 4-substituted pyrazolone derivatives.