Anaesthesia-induced malignant hyperthermia (MH) may be caused by specific gene defects in the skeletal muscle ryanodine receptor. We have studied the frequency of occurrence of the C1840T mutation, analogous to the porcine mutation, and three mutations associated both with MH and central core disease (G7301A, C487T and C1209G). We investigated skeletal muscle specimens from up to 137 patients testing negative and 101 patients testing positive for MH susceptibility by the North American MH Group protocol. The presence or absence of the mutations was determined by polymerase chain reaction and restriction enzyme digestion. The frequencies of occurrence of the C1840T and C487T mutations were 2% and 1%, respectively, in MH-positive subjects and were the only two mutations identified. One subject with central core disease did not have any of the three mutations examined associated with this disorder. Therefore, the porcine and central core disease-associated mutations examined in the ryanodine receptor account for a small proportion (approximately 3%) of MH-positive diagnoses. The mutations examined did not occur in any of the MH-negative patients, supporting an association between defects in the ryanodine receptor and a positive diagnosis for MH.(ABSTRACT TRUNCATED AT 250 WORDS)