Tissue specimens from twenty patients with squamous cell carcinoma of the larynx were obtained. The tissue was retrieved from total laryngectomy specimens , and processed for histological and histopathological characterization. Samples of squamous cell carcinoma were subjected to this study. Full term normal placentae were used in comparison. Histochemical study of alkaline phosphatase was done using simultaneous Azo coupling method while biochemical studies were done using disodium phenyl phosphate as a substrate with the appropriate preparation procedure. The inhibition profile of alkaline phosphatase activity was studied using heat inactivation, L-Amino acids and levamisole. The specific activity of alkaline phosphatase from cancerous laryngeal tissue was 8.9 mu/mg protein compared to 154.7 mu/mg protein in the placenta. The alkaline phosphatase was localized histochemically in tumor cells (tumor-specific) , blood vensels (vascular) and fibrous tissue (interstitial). The tumor specific phosphatase was sensitive to inhibition by Phenyldanme, Leucine and to a lesser degree by Tryptophan and Levamisole. Placental alkaline phosphatase on the other hand was more resistant to Leucine and Levamisole and more sensitive to Phenylalanine and Tryptophan. Biochemical estimation of alkaline phosphatase in cancerous laryngeal tissue combined with Inhibition studies showed that the tumor-specific activity of alkaline phosphatase constitutes about 16% of the total alkaline phosphatase activity while the major isoenzyme was the vascular alkaline phosphatase , and around one third of alkaline phosphatase activity was attributed to the interstitial enzyme. The characterization and localization of these isoenzymes were described and compared with thatt of the placenta. The significance and implications of the above findings were put forward.