Sixty patients undergoing humeral surgery with posterior incision and medial arm skin graft harvest were randomized to receive either a subpectoral intercostal plane block at the second rib (n=30) or a pectoserratus plane block at the fourth rib (n=30), following a supraclavicular brachial plexus block. The primary outcome was the time of onset of intercostobrachial nerve (ICBN) block. Secondary outcomes included the time taken to perform the block and the block failure rate. Outcomes were assessed over a 15-minute period after block administration. Overall, the results revealed that the subpectoral block group had a significantly faster onset, shorter procedure time, and 100% success rate compared to the pectoserratus block group, which had a 30% failure rate. These findings suggest that the subpectoral approach is superior in terms of efficacy and speed for ICBN blockade.