Since most common diseases have been shown to be influenced by inherited variations in our genes, completion of the Human Genome Project and mapping of the human genome single-nucleotide polymorphisms will have a tremendous impact on our approach to medicine. New developments in genotyping techniques and bioinformatics, enabling detection of single-nucleotide polymorphisms, already provide physicians and scientists with tools that change our understanding of human biology. In the near future, studies will relate genetic polymorphisms to features of critical illnesses, increased susceptibility to common diseases, and altered response to therapy. Novel insights into the contribution of genetic factors to critical illnesses and advances in pharmacogenomics will be used to select the most effective therapeutic agent and the optimal dosage required to elicit the expected drug response for a given individual. Implementation of genetic criteria for patient selection and individual assessment of the risks and benefits of treatment emerges as a major challenge to the pharmaceutical industry.