Final answer:
Block 33a of the CMS-1500 claim contains the provider's NPI (National Provider Identifier).
Step-by-step explanation:
Block 33a of the CMS-1500 claim contains the provider's NPI (National Provider Identifier). The NPI is a unique identification number assigned to healthcare providers by the Centers for Medicare and Medicaid Services (CMS). It is used to identify individual providers, group practices, and healthcare organizations.