Absolute linkage between the gene, on chromosome 19, for the calcium release channel (CRC) of the sarcoplasmic reticulum in skeletal muscle and malignant hyperthermia (MH) has been reported by other workers. In the present study of three Swedish Families informative with respect to this linkage relationship, definite recombinants were found in two families. We conclude that mutations in other genes than the CRC gene can cause the clinical picture of MH. Accordingly, MH appears to be genetically heterogeneous.