In this work, analysis of some drugs of different pharmacological action (Aripiprazole , lamivudine, lomefloxacin HCl, losartan potassium, pantoprazole sodium, rabeprazole sodium, sibutramine HCl and sumatriptan succinate) were studied. The aim of this work is to develop, optimize and validate sensitive, precise and accurate methods for determination of the investigated drugs, either in pure form or in their pharmaceutical formulations with low cost depending on the availability of chemicals and equipments. The investigation includes usefulness of certain spectroscopic techniques including: spectrophotometry, atomic absorption spectrometry. Conductometric and potentiometric techniques were also applied. The thesis consists of five parts: Part I: This part is concerned with the demonstration of molecular structure, physical and pharmacological properties of the studied drugs and also a theoretical basic background review on the previous methods of the assay of the cited drugs. Part II: This part describes charge transfer complexation reactions and it is divided into three chapters: Chapter (1): This chapter describes spectrophotometric determination of aripiprazole, sumatriptan succinate, lamivudine and rabeprazole sodium through charge transfer complexation reactions with p.chloranilic acid, 3-dichloro-5,6-dicyano-pbenzoquinone and iodine. Results obtained were compared with those of comparison methods Chapter (2): This chapter is concerned with studying the conductometric determination of aripiprazole, sumatriptan succinate, lamivudine and rabeprazole sodium through charge transfer complexation reactions with p.chloranilic acid and 3-dichloro-5,6- dicyano-p-benzoquinone Results obtained were compared with those of comparison methods. Chapter (3): This part demonstrates Potentiometric determination of aripiprazole, sumatriptan succinate, lamivudine and rabeprazole sodium through charge transfer complexation reactions with p.chloranilic acid. Results obtained were compared with those of comparison methods. Part III: This part describes complexation reaction with phosphomolybdic acid and it is divided into three chapters Chapter (1): This chapter demonstrates spectrophotomteric determination of sibutramine HCl, sumatriptan succinate and lomefloxacin HCl with PMA-Co(II)-EDTA. Results obtained showed good agreement with those obtained by comparison methods Chapter (2): This chapter describes the Spectrophotomteric determination of sibutramine HCl, sumatriptan succinate and lomefloxacin HCl with PMA. The obtained results were compared with those of comparison methods. Chapter (3): This chapter is concerned with conductometric determination of sibutramine HCl, sumatriptan succinate and lomefloxacin HCl with PMA. The data given are statistically compared with those of comparison methods. Part IV: This part describes complexation reaction bismuth tetraiodide and it is divided into two chapters Chapter (1): This chapter demonstrates spectrophotometric and atomic absorption spectrometric methods for the determination of lomefloxacin HCl, pantoprazole sodium and sumatriptan succinate through precipitation with bismuth tetraiodide. Results obtained were compared with those of comparison methods. Chapter (2): This chapter is concerned with conductometric determination of lomefloxacin HCl, pantoprazole sodium and sumatriptan succinate through precipitation with bismuth tetraiodide. The data given are statistically compared with those of comparison methods. Part V: This part describes conductometric determination of losartan potassium, pantoprazole sodium, rabeprazole sodium and sumatriptan succinate with silver nitrate. The obtained results were compared with those of comparison method