BACKGROUND : Ankle joint function in a paretic limb has a fundamental impact on mobility. Return of joint function is a measure of early poststroke physical rehabilitation. This study aims to assess the suitability of using the isometric protocol for objective evaluation of flexor and extensor muscle strength in the paretic limb of poststroke patients. METHODS : 34 patients (F: 9, M: 25) aged 51-79 years with hemiparesis following an acute ischemic stroke and 34 healthy controls were examined using the isometric protocol measured on the Biodex System®. The following parameters were analyzed: peak torque [PT], average torque [AVGT], average torque/body weight [AVGT/BW] for flexors and extensors, and AVGT flexor/AVGT extensor [agonist/antagonist ratio] of the paretic foot, the nonparetic foot and foot of healthy controls using three foot-shank positions (15°, 0°, and - 15°) prior to rehabilitation commencement and at its completion 16 weeks later. RESULTS : Prior to rehabilitation commencement, nonparetic foot differed significantly (p < 0.05) from healthy foot controls in all parameters and all positions for flexors and in all positions for foot-shank positions of 0° and - 15° for extensors. At rehabilitation program completion the following parameters increased significantly for the paretic foot: PT, AVGT, and AVGT/BW for foot extensors in all tested positions, and PT for foot flexors in foot-shank position of - 15°. The nonparetic foot however, showed no significant difference following rehabilitation regardless parameter or foot position tested for flexors and extensors alike. Prior to rehabilitation agonist/antagonist ratio in the paretic foot differed significantly from corresponding parameter in the control group for the foot-shank positions of 15° and 0°, whereas at rehabilitation completion, the two groups showed significant difference only in foot-shank position of 0°. CONCLUSIONS : In the early period following stroke, there is a significant strengthening of the paretic limb, but no improvement in the strength of nonparetic limb.