Mo. Rev. Stat. § 194.250: Document of gift, procedure.

1. A person authorized to make an anatomical gift under section 194.245 may make an anatomical gift by a document of gift signed by the person making the gift or that person's oral communication that is electronically recorded or is contemporaneously reduced to a record and signed by the individual receiving the oral communication.

2. Subject to subsection 3 of this section, an anatomical gift by a person authorized under section 194.245 may be amended or revoked orally or in a record by any member of a prior class who is reasonably available. If more than one member of the prior class is reasonably available, the gift made by a person authorized under section 194.245 may be:

(1) Amended only if a majority of reasonably available members agree to the revoking of the gift; or

(2) Revoked only if a majority of the reasonably available members agree to the revoking of the gift or if they are equally divided as to whether to revoke the gift.

3. A revocation under subsection 2 of this section is effective only if, before an incision has been made to remove a part from the donor's body or before invasive procedures have begun to prepare the recipient, the procurement organization, transplant hospital, or physician or technician knows of the revocation.