The hydrazones of hydralazine hydrochloride with various aromatic aldehydes were prepared and their spectral properties were examined. On the basis of the above examination, a colorimetric determination of hydralazine hydrochloride with p-dimethylaminocinnamaldehyde based on solvent extraction (CHCl₃) was developed. The calibration curve obtained was linear up to 9.8 μg/ml of hydralazine hydrochloride. The method was successfully applied for the analysis of commercial pharmaceutical preparations (tablet and injection). The contents found were 106±2% (tablet) and 100±1% (injection) of the labeled values.