The post-translational methylation of histidine to form 3-methylhistidine (3MH) is a modification principally found in contractile proteins, and thus, the level of free 3MH has been used to monitor muscle protein turnover. This work describes procedures for the capillary electrophoretic separation and determination of the phenylthiohydantoin (PTH) derivative of 3MH using uncoated fused-silica capillaries. The procedure described here utilized UV detection and resulted in a linear standard curve in the range of 2-15 pmole, which is more sensitive than previously reported HPLC methods using fluorescent detection. In addition, good agreement for theoretical amounts of 3MH in hydrolyzed rabbit skeletal muscle actin and myofibril preparations from bovine skeletal muscle cells was found.