Many studies are in progress worldwide to elucidate the genetics of NIDDM. Nevertheless, few articles are available that combine the interdisciplinary fields of medicine, genetics, physiology, and statistics in order to provide the scientific rationale for such an endeavor. Here we describe the methodology and background necessary to study the genetics of NIDDM and discuss how to analyze the data. We also provide a detailed bibliography for researchers and a glossary for those who are not experts in the field. In particular, we wish to emphasize the analysis of intermediate quantitative traits as a means to dissect the genetic basis of NIDDM.