Missouri Revised Statutes Title XXXVI. Statutory Actions and Torts § 537.764. State of the art, defined--affirmative defense in cases of strict liability for failure to warn--burden of proof on party asserting defense--action for negligence, when

1. As used in this section, “state of the art” means that the dangerous nature of the product was not known and could not reasonably be discovered at the time the product was placed into the stream of commerce.

2. The state of the art shall be a complete defense and relevant evidence only in an action based upon strict liability for failure to warn of the dangerous condition of a product. This defense shall be pleaded as an affirmative defense and the party asserting it shall have the burden of proof.

3. Nothing in this section shall be construed as limiting the rights of an injured party to maintain an action for negligence whenever such a cause of action would otherwise exist.

4. This section shall not be construed to permit or prohibit evidence of feasibility in products liability claims.