ALTHOUGH the histology and ultrastructure of smooth muscle cells have been studied extensively there is little direct evidence concerning their mechanical properties. Their small size^1,2 and lack of tendon connections have prevented them from being mounted on a myograph, as has been done with striated muscle fibres³. Moreover, their multiplicity and optical properties make it difficult to visualise them in whole smooth muscle preparations. Although isolated smooth muscle cells^4–6 can be seen to contract when stimulated, it has not been possible to measure the forces they develop. There are, therefore, still serious doubts about the extent to which the mechanical properties of whole smooth muscle preparations are an accurate reflection of the properties of smooth muscle cells. We have therefore developed a technique to obtain mechanical data from a smooth muscle preparation which only contains about 1,000 smooth muscle cells, and which is thin enough for the cells to be visualised by Nomarski interference microscopy⁷. This technique provides for the first time the means to study the mechanical properties of smooth muscle cells in situ.