Type 1 von Willebrand disease (vWD) is an autosomal dominant bleeding disorder of variable penetrance. It is characterised by a mild to moderate bleeding tendency and a quantitative deficiency of von Willebrand factor (vWF) with the full range of vWF multimers. Few mutations have been described which account for the mode of inheritance in dominant vWD type 1. We screened the vWF multimerization domains (regions D1-D3 of the vWF gene) of 12 unrelated patients with dominant vWD type 1 to investigate the hypothesis that multimerization of vWF sub-units may be inhibited or reduced by a "dominant negative" mechanism. Platelet-derived RNA was reverse transcribed and the resulting vWF cDNA amplified by the polymerase chain reaction (PCR) in a series of overlapping fragments. These were subjected to a combination of single-strand conformation polymorphism (SSCP) and heteroduplex analysis. This approach identified mobility shifts on acrylamide gels that represented 12 distinct SSCP and/or heteroduplex patterns in our patient group. DNA sequencing of the region encompassing each mobility shift showed these variants to represent previously described polymorphisms within the vWF coding sequence. Examination in all 12 patients for the previously described G3389T and T3445C mutations proved negative. The molecular pathology of classical type 1 vWD remains enigmatic, mutations having been identified in only a small minority of patients. A common mechanism underlying this disease state has still to be elucidated.