Plants are very complex in their composition due to influence of environment, climate, and growth conditions. Due to complex nature and inherent variability of the constituents of plant based drugs, it is difficult to establish quality control parameters. Standardization is a tool in the quality control process. When standardization is not adequately done by chemical or physical means, Pharmacological methods are used. The assays of herbal formulations on living animal and on their intact or isolated organs indicate their therapeutic activity.