Prolyl Ohgopeptidase (PO) was purified from human saliva and partially characterised. The techniques employed during purification were Phenyl Sepharose Hydrophobic Interaction and Anion Exchange Chromatography, where the peptidase could be isolated from this low protein source. The enzyme was shown to have a monomeric molecular weight o f81,000 Da, which was also believed to be the native molecular weight DTT had a considerable enhancing effect on PO activity, suggesting the presence of thiol groups as part of cysteine residues at or near the enzyme’s active site. A preference was shown for neutral pH ’s with an optimum at pH 7 5 in potassium phophate buffer. The peptidase’s activity proved to be quite unstable at physiological temperature, even when stabilising agents were included Similarly significant enzyme activity was lost at frozen storage conditions. Therefore it is probable that PO is secreted into saliva in an inherently unstable form. Dipeptidyl Peptidase IV (DPPIV) was purified to homogeneity from bovine serum. The chromatographic techniques used were Phenyl Sepharose Hydrophobic Interaction, Sephacryl S300 Gel Filtration, Anion Exchange and G100 Gel Filtration, producing an overall purification factor of 257. SDS PAGE resulted in a monomeric weight of 70,740 Da while Size Exclusion Chromatography generated an average native molecular weight determination of 302 000 Da Therefore it is proposed that the enzyme was a tetramer. A glycoprotein stain of a SDS PAGE gel suggests that DPPIV is glycosylated\ which adds to the estimated molecular weight. DPPIV remains active over a broad pH range with a preference for neutral pH, while the isoelectric point was estimated at 4 7. Although the enzyme is generally classified as a serine protease, it was not inhibited by any serine protease inhibitors. The enzyme was inhibited by the phenanthrolmes, which are metallo-protease inhibitors but remained unaffected by the metal chelators. Therefore is not believed that DPPIV is a metallo protease but its activity could be reduced due to enzyme surface binding. This was confirmed by the minimal effect metal ions had on activity. Substrate Specificity of DPPIV via HPLC proved that DPPTV is capable of sequential cleavage of fi- Casomorphin, Substance P and Enterostatin Analogues of C-Reactive Protein (CRP), Insulin-like Growth Factor (IGF) and Neuropeptide Y were also shown to be susceptible to DPPTV cleavage The peptidase cleaved the standard DPPTV substrate, Gly-Pro-MCA with a Km of 38 4fjM, while Lys-Pro-MCA was hydrolysed with a KM value of 103uM. DPPTV was specifically inhibited by both Diprotm A and B, where the mode of inhibition was observed to be non-competitive, generating K, ’s of 1 4x10 4Mfor both inhibitors Ile-Thiazohdide and Ile-Pyrrohdide both inhibited DPPTV competitively with estimated inhibition constants of 3 7x10 ?M and 7 5x10 7M determined respectively Inhibition studies of two prohne containing peptides, /3-Casomorphm and Substance P, generated two different modes of inhibition for the two peptides fi-Casomorphin inhibited competitively with an average K, of 1 1x1 O'4M, while Substance P inhibited un-competitively generating an inhibition constant of5 5x10 4M.