An investigation of the biomechanical properties of the cat patellar tendon (PT) is presented. Standard in vitro techniques were used to quantify stiffness, K, ultimate force, F_UT, and ultimate elongation, ΔL_UT, of matched pairs of PT specimens. Mean (±SD) values of 320 (±43) N mm^-1, 870 (±160) N and 4.8 (±1.6) mm were determined for K, F_UT and ΔL_UT, respectively. Mean left-right differences were not found to be significant (P > 0.4). Tissue stress and strain were quantified from failure tests. An elastic modulus, E, of 1335 (±221) MPa was observed in these tests. A new in situ non-contact technique for measuring the force-elongation behaviour of the intact PT in an animal model was developed. The technique was used to characterise the mechanical response of PT tissue in a controlled loading protocol. An in situ modulus, E, of 1509 (±229) MPa was estimated from a single experiment.