We carried out a segregation analysis comparing the inheritance of collagen gene markers and joint hypermobility syndrome in two extended families. Our results exclude the genes encoding type III (COL3A1), type V alpha 2 chain (COL5A2) and type VI alpha 3 chain (COL6A3) unambiguously in both families. The simultaneous exclusion of both the type 1 alpha 1 and alpha 2 chain genes in the same family was not possible: COL1A1, but not COL1A2 was excluded in one and COL1A2, but not COL1A1 was excluded in the second. There was no suggestion of strong linkage to either of these loci. These data do not support the hypothesis that JHS in these families is caused by mutations in these collagen genes.