Drug discovery is a challenging field. It involves team work of several experts including medicinal chemists, natural chemists, pharmacologists, toxicologists, clinicians etc to generate a safe and biologically active drug. In the drug discovery programme, medicinal plants play a key role and are a source of novel molecules. The knowledge of folk medicine and ethnopharmacological studies of plants play a significant role in the development of primary screening methods in drug discovery.Enzymes are the targets for many drugs because of the simplicity of enzyme based assays. It involves the interaction with substrate to form the product. The inhibitor will also interact with the enzyme, hence decreasing the rate of reaction. The enzyme inhibition assays have prompted us to do a primary screening of the methanolic extracts of plants commonly used in Pakistan. Therefore these studies were designed to investigate if any a target drug is present in a plant and to which extent it is there to inhibit a particular enzyme of therapeutic importance.