World super-bantamweight champion Rey Vargas and number-one ranked flyweight Julio Cesar Martinez will not face sanctions after positive doping tests.
Mexicans Vargas, 28, and Martinez, 24, returned trace elements of Clenbuterol.
The tests were done by the Voluntary Anti-Doping Association but the WBC said the amounts of Clenbuterol were "so small" that no action was taken.
"The amounts found in the tests are not sufficient to register any performance-enhancing benefit," the WBC said.
"The muscle-forming drug is commonly found in many meat products throughout Mexico.
"Both Vargas and Martinez said that there was no conscious or deliberate intent to take Clenbuterol.
"Previous positive tests for Clenbuterol have been registered by Saul 'Canelo' Alvarez and Francisco 'Bandido' Vargas, also in very small amounts meaning accidental ingestion via food."
Vargas won his WBC super-bantamweight from Britain's Gavin McDonnell in Hull in 2017 and has defended it five times since.
Martinez is ranked number one at flyweight by the WBC. He looked to have won the WBC flyweight title from Charlie Edwards in August but the bout was deemed a no contest as a result of him landing a punch when the Briton was on the canvas.