The surface pH of skeletal muscle has been confirmed to be a sensitive indicator of peripheral muscle blood flow, but the development of a better electrode has been required. As a consequence, a unique and minute sensor was developed to measure muscle pH/PCO2. The purpose of this article was to evaluate this new monitoring device experimentally and clinically in order to clarify its effects, usefulness and specificity. Our experimental and clinical results showed that placement and measurements using the muscle pH/PCO2 monitor were easily and quickly accomplished without any complications. This small sensor provided an accurate assessment of vital physiologic functions and gave an early warning of clinical deterioration. The new monitor should be useful in pediatric surgery clinical management.