37 CFR § 42.65 - Expert testimony; tests and data.

---
identifier: "/us/cfr/t37/s42.65"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "37 CFR § 42.65 - Expert testimony; tests and data."
title_number: 37
title_name: "Patents, Trademarks, and Copyrights"
section_number: "42.65"
section_name: "Expert testimony; tests and data."
chapter_name: "UNITED STATES PATENT AND TRADEMARK OFFICE, DEPARTMENT OF COMMERCE"
subchapter_number: "A"
subchapter_name: "GENERAL"
part_number: "42"
part_name: "TRIAL PRACTICE BEFORE THE PATENT TRIAL AND APPEAL BOARD"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "35 U.S.C. 2(b)(2), 3, 6, 21, 23, 41, 134, 135, 143, 153, 311, 312, 314, 316, 318, 321-326, 328; Pub. L. 112-29, 125 Stat. 284; and Pub. L. 112-274, 126 Stat. 2456."
regulatory_source: "77 FR 48669, Aug. 14, 2012, unless otherwise noted."
cfr_part: "42"
---


# 42.65 Expert testimony; tests and data.

(a) Expert testimony that does not disclose the underlying facts or data on which the opinion is based is entitled to little or no weight. Testimony on United States patent law or patent examination practice will not be admitted.

(b) If a party relies on a technical test or data from such a test, the party must provide an affidavit explaining:

(1) Why the test or data is being used;

(2) How the test was performed and the data was generated;

(3) How the data is used to determine a value;

(4) How the test is regarded in the relevant art; and

(5) Any other information necessary for the Board to evaluate the test and data.