A series of 4-arylhydrazono-1-carbamoyl-3-methyl-2-pyrazolin-5-ones have been synthesised, for evaluation as antidiabetic agents, from the appropriate aryldiazonium salts and 1-carbamoyl-3-methyl-2-pyrazolin-5-one. A series of 4-arylazo-1-(2,4-dinitrophenyl)-3-methyl-5-phenylpyrazoles were obtained by the cyclisation of 2-arylhydrazono-1-phenylbutane-1,2,3-triones with 2,4-dinitrophenylhydrazine.