Malignant hyperthermia is a potentially fatal pharmacogenetic disorder triggered by volatile anesthetics (halothane, enflurane, isoflurane) and/or succinylcholine. The inheritance of malignant hyperthermia susceptibility is thought to be autosomal dominant and the incidence could be as high as 1:10,000. The only generally accepted diagnostic method at present involves a muscle biopsy followed by in-vitro halothane and caffeine contracture tests. 100 individuals from 45 families who were considered to be potentially malignant hyperthermia-susceptible were investigated from 1986 to 1990 by in-vitro muscle contracture tests using the protocol of the European Malignant Hyperthermia Group. Of 45 families analyzed, 28 had at least one person who was susceptible to malignant hyperthermia with a total of 64 malignant hyperthermia-susceptible individuals. 36 subjects in the 45 families were normal. In addition, our study shows that a femoral nerve block can be used in outpatients as a reliable anesthetic technique to perform biopsies from the vastus medialis muscle for malignant hyperthermia screening.