Malignant hyperthermia (MH) is currently diagnosed by the caffeine-halothane contracture (CHC) test. In a previous study, this test was used to establish linkage between the human gene for MH susceptibility and the ryanodine receptor (RYR) gene. The current study extends the genetic linkage analysis to a large French-Canadian kindred. In this family, genetic linkage between RYR and MH genes was not demonstrable using the currently recommended limits of normal for the CHC test in the identification of MH-susceptible individuals. With CHC test threshold limits below those currently recommended, however, complete linkage between the RYR and MH genes was seen. Comparisons of CHC test results with genetic linkage studies will increase the diagnostic accuracy of both tests as well as generate new insights into the biology of MH.