New methods for studying the genetic information of humans in health and disease are emerging from basic science laboratories. Because these approaches are yielding fundamental insights for diagnosing and treating disease, it is important that practitioners begin to understand these methods and how they are used. Methods for genetic analysis using recombinant DNA techniques consist of isolation, separation, propagation in microorganisms and molecular hybridization of DNA. The study of RNA allows determination of gene expression. These methods are being used to understand cancer, identify hereditary illness, produce pharmaceuticals and diagnose common clinical problems, such as infectious diseases.