High-frequency alternating current (HFAC) applied to a peripheral nerve can reversibly block skeletal muscle contractions. We evaluated the ability of HFAC delivered via intrafascicular electrodes to selectively block activation of targeted muscles without affecting activation of other muscles. Utah slanted electrode arrays (USEAs) were implanted into the sciatic nerves of five cats, and HFAC was delivered to individual USEA electrodes. The effects of HFAC block were monitored by recording evoked electromyograms (EMGs) and three-dimensional endpoint forces. In each animal, activity evoked in targeted muscles by nerve cuff stimulation could be selectively abolished by HFAC delivered via individual USEA electrodes. Two mechanisms of blockade were evoked: selective neuromuscular blocks were achieved with 500-8000-HZ HFAC, and selective nerve conduction block was achieved in one animal using 16-kHZ HFAC. These results show that intrafascicular HFAC can be used to block selected muscles independent of activation of other muscles.