The ratio of cell volume to cell surface area (V/A) has been measured by electron microscopy, for smooth muscle cells of the guinea-pig taenia coli. The extent of shrinkage which occurs during processing for electron microscopy has been estimated using Archimedes' principle. The corrected ratio of V/A is 0.8 mum which is lower than previously published estimates for this tissue. The contribution of the surface vesicles to V/A was not included in the present estimate, but the extra surface area contributed by these organelles would lower V/A even more.