Drug design is an integrated developing discipline which portends an era of ‘tailored drug’. It involves the study of effects of biologically active compounds on the basis of molecular interactions in terms of molecular structure or its physico-chemical properties involved. It studies the processes by which the drug produce their effects, how they react with the protoplasm to elicit a particular pharmacological effect or response how they are modified or detoxified, metabolized or eliminated by the organism.Disposition of drugs in individual region of biosystems is one of the main factors determining the place , mode and intensity of their action . The biological activity may be “positive” as in drug design or “negative” as in toxicology. Thus drug design involves either total innovation of lead or an optimization of already available lead. These concepts are the building stones up on which the edifice of drug design is built up.