In December 1994, when Ernesto Zedillo took office, he discovered that
the guy who passed the presidency to him had taken off to Ireland with
half of our country’s money. Zedillo, who holds a doctorate in economics
from Yale, decided (in collusion with his predecessor, who holds a
doctorate in economics from Harvard) to hide this devaluation by
demonetizing our currency when he took office.

 As of 1 January 1996,
only the Banco de Mexico has accepted pre-Zedillo pesos, and at one
one-thousandth of their face value. Or, worthless! Well, pennies lets say. Almost worthless.

Zedillo referred to his devaluation as “nuevos pesos”. During his
presidency our prices were often expressed as “NP$200”. He put a
grandfather clause in his devaluation such that “NP” would change to
“peso” with the demonetization. During that period, we took our “old”
pesos to any branch of the Banco de México to exchange them for shiny
New Pesos at the rate of one thousand old ones for one new one.

The Banco de México still maintains this exchange program, albeit in
only four hundred of its branches throughout the country. If you have
hundreds of thousands of old pesos, it might be worth it to you to make
the exchange.

If you hold a bank account anywhere in Mexico, your bank is required by
federal regulations to accept the deposit of your old pesos at 1:1000
and to exchange them for you with the Banco de México.

Old pesos in crisp uncirculated condition can have a numismatic value
far in excess of their demonetized face value. For that you would need
to investigate the collectors’ market by googling a phrase along the
lines of “world banknotes”.

So if your parents have some pesos from that trip they took 50 years ago – throw them away!