N-acetylation of certain drugs with an aromatic amine group exhibit a bimodel character and the population can be classified as fast and slow acetylators according to their abilities to metabolize these drugs through acetylation. The racial differences among different populations are the major problems in dealing with certain drugs. The dosage regimen evaluated to be the most appropriate for a population group may not be as effective for another population group in a different environment. There are at least a dozen of genetically controlled conditions which produce unusual response to various drugs. Rapid and slow acetylation of amine drugs, deficiencies of plasma pseudocholinesterase and glucose6phosphate dehydrogenase are reported to exist. Among these, Polymorphic acetylation has a wide spread implication. Significance of this phenomenon becomes apparent in case of drugs which undergo acetylation conjugation as part of their metabolism, acetylation reaction, phenotypes in drug metabolism, acetylation reaction, phenotypes in drug acetylation, distribution of phenotypes and effect of acetylation status in human.