Combined molecular and epidemiological studies are advancing our understanding of the genetic basis of multifactorial diseases. Several of the results obtained during the past year highlight methodological issues associated with these approaches. For example, the affected sib-pair method has been applied successfully to detect linkage between the angiotensinogen gene and susceptibility to hypertension, and a large multi-centre epidemiological study has demonstrated association of a polymorphism of the angiotensin-converting enzyme gene with increased risk of myocardial infarction. The study of Mendelian forms of multifactorial diseases has also led to many new results. These include the characterization of mutations in the glucokinase gene in maturity onset diabetes of the young, localization to chromosome 2 of a gene involved in familial colon cancer, and localization to chromosome 19 of a gene responsible for hemiplegic migraine. New insights have been provided into the genetics of multifactorial disorders such as diabetes and hypertension through the study of animal models. Localization of susceptibility loci in such models has recently led to the identification of new candidate genes that may be implicated in disease.