To interpret data from the compression experiment (micromanipulation), the initial radial stretch ratio and the wall thickness to cell radius ratio are required. Methods have been developed to measure these parameters for baker's yeast (Saccharomyces cerevisiae) prior to compression experiments. The initial radial stretch ratio was found using osmotic theory to interpret measurements of cell-volume change as a function of external osmotic pressure. Initial wall thickness to cell radius ratio was found using image analysis measurements of cell-section photographs taken with transmission electron microscopy (TEM). A novel mathematical model was developed to correct for random slicing during TEM sample preparation. The effects of osmotic pressure (0-0.8 MPa) and compression rate (1.03-7.68 mu m/s) on the bursting force, deformation at bursting, and cell diameter were quantified. Squeeze-hold experiments showed that force relaxation occurred. Bursting force, deformation at bursting, and cell diameter were all significantly affected by osmotic pressure (P < 0.05) but were unaffected by compression rate (P greater than or equal to 0.05). Bursting force was found to be correlated with deformation-at-bursting but was independent of cell diameter. These data are analysed in further detail in an accompanying paper (part II).