Six large families with classical Marfan syndrome were studied using markers on chromosomes 1 and 11. Two of three families tested showed negative scores using DIS7 but a third family gave a positive score (0.92) at 0=0*1. The other chromosome 1 markers typed (MUCI, NGFB, DIS8) excluded close linkage. Negative lod scores with two chromosome 11q22 markers (DIIS84, DIIS148) excluded at least 20 cM in this area (Z= <-2), which was chosen for study as two enzymes responsible for coliagen degradation (coliagenase and stromelysin) are localised to this region.Marfan syndrome is a dominantly inherited connective tissue disorder affecting primarily the skeletal, ocular, and cardiovascular systems. The estimated prevalence is 6/100 000, with 25% of cases resulting from new