Methods for assessing viscoelastic properties of soft tissues are based on detecting an inflection point on a pressure-time plot when air is aspirated from a cavity placed over the tissue sample. A small diameter tube through which air aspiration is conducted is ultimately closed off by tissue being drawn into the cavity causing an abrupt change in pressure slope. First or second derivatives of the pressure-time plot can be used to detect the inflection point. Repeating the test with a different aspiration rates or after a predetermined relaxation time allows determining tissue viscosity and tissue creep in addition to tissue elasticity expressed as Young's modulus.