Exhibit 10.1 FOURTH SUPPLEMENTAL INDENTURE SUPPLEMENTAL INDENTURE dated as of March 19, 2003, (this "Fourth Supplemental Indenture"), among UNILAB CORPORATION (f/k/a Quest Diagnostics Newco Incorporated), (the "Additional Subsidiary Guarantor"), QUEST...Fourth Supplemental Indenture • April 30th, 2003 • Quest Diagnostics Inc • Services-medical laboratories • New York
