The presence of elastic fibres in the extracellular matrix (ECM) provides 
physiologically important elastic properties for many tissues. Until recently, 
microfibrils, one component of the ECM, were thought primarily to serve as a 
scaffolding on which elastin is deposited during development to form elaunin 
fibres [1]. The most prominent protein that forms mammalian microfibrils is 
fibrillin. It is known that mutations in the fibrillin gene cause a heterogenous 
connective tissue disease called Marfan syndrome [2], so information on 
mechanical properties of microfibrils or their role in tissue function would be 
useful. Microfibrils are also found in the ECM of some invertebrate tissues, and 
there is growing evidence that the protein forming the structure is homologous 
to mammalian fibrillin [3,4]. It has been shown that the microfibril-based 
arterial wall of the lobster has viscoelastic properties [5], and we have now 
utilized this primitive artery to measure the modulus of elasticity of 
microfibrils. It is similar to that of the rubber-like protein elastin.