The evaluation of knee motion is an important step for correct diagnoses and optimal surgical reconstructions, but controversial opinions still remain about the most suitable numerical method for the elaboration of clinical kinematic tests. In this paper, we present a comparison of three methods applied to an experimental animal study (Grood and Suntay method [Grood, E.S. and Suntay, W.J. (1983) "A coordinate system for the clinical description of three-dimensional motions: application to the knee", J. Biomech. Engng, 105, pp. 136-144], Helical Axes method [Blankevoort, L., Huiskes, R. and de Lange, A. (1990). "Helical axes of passive knee joint motions", J. Biomech., 23 pp. 1219-1229] and Functional method [Martelli, S., Zaffagnini, S., Falcioni, B. and Marcacci, M. (2000). "Intraoperative kinematic protocol for knee joint evaluation", Comput. Methods Programs Biomed., 62 pp. 77-86]). The study shows the numerical differences among the three protocols and evaluates their performances and repeatability during clinical tests, i.e. laxity measurements and passive range of motion. The Functional method gives the optimal compromise among accuracy, clinical interpretability and ease of use for intraoperative kinematic evaluations.