New high performance liquid chromatography (HPLC) and thin layer densitometry (TLC) methods are developed for quantification of cinnarizine in dosage forms in the presence of its photo-degradation products and related substances and in the presence of its metabolites in serum. Mobile phases consisting of benzene-methanol-formic acid (80:17:3) and methanol-acetate buffer of pH 4 (70:30) are satisfactorily used for resolution of cinnarizine from associated substances by TLC and HPLC techniques, respectively. The lower detection limits are 16 and 10 ng microl(-1) of cinnarizine with standard deviations of 1.3 and 1.1% with TLC and HPLC, respectively. The methods are used for assessment of drug purity, stability, bioavailability, bioequivalency and tablet dissolution rate. Four cinnarizine related substances and six drug degradation products are isolated and identified by infrared and mass spectrometry. The results obtained by both techniques are in good agreement and offer the advantages of reproducibility and accuracy.