The aim of the present study was to investigate the reliability of different methods used for isokinetic testing of calf muscle strength and endurance. The detailed evaluation of test-retest reliability serves the purpose of establishing reliable research tools when evaluating patients who have sustained an Achilles tendon rupture. The test-retest reliability of isokinetic measurements at the ankle for eccentric and concentric muscle action was calculated in ten healthy male volunteers using intra-class correlation (ICC) and coefficient of variation (CV). Three different positions were compared at the angular velocities of 30 degrees /s and 180 degrees /s for right and left ankles. The ICC for plantar flexion was 0.37-0.95, whilst it was 0.00-0.96 for dorsiflexion. The corresponding CVs were 4.0-19.9 and 2.4-19.8 respectively. The test-retest reliability of standardised heel-raises, Achilles tendon width, calf circumference and ankle range of motion revealed ICC values of 0.71-0.98 and CVs of 0.67-19.1. The test-retest interval was 5 to 7 days. We conclude that all three positions studied for the isokinetic evaluation of calf muscle function are equally reliable concerning plantar flexion at the ankle joint. The same level of reliability was also found in the evaluation of the standing heel-raise test and the isokinetic dorsiflexion test, except for dorsiflexion in the supine position. The reliability of the investigated methods was only fair despite the use of a detailed and standardised test protocol.