The quality of results obtained with molecular biology techniques depends on the control of preanalytical and analytical error associated with such techniques. Preanalytical error can be introduced during the isolation of DNA and RNA. The type of detergent used in cell lysis can affect the amplification of DNA by techniques such as the polymerase chain reaction(PCR). Ribonuclease(RNase) contamination is a serious problem in the isolation of undegraded RNA, and, thus, this enzyme should be inhibited. Anticoagulants used for blood collection can affect the quality of results with molecular biology techniques. The control of contamination from the working environment is essential to the minimization of preanalytical, analytical and postanalytical error. Molecular biology techniques for a wide range of clinical laboratory tests have been established in hospitals such as clinical laboratory tests for infections, molecular diagnoses of leukemia and aberrant genes in metabolism.