The National Gallery is limiting visitor numbers to a forthcoming exhibition to stop it from being "overrun".
Admissions to the Leonardo da Vinci exhibition, in the gallery in central London's Trafalgar Square, will be fixed at 180 people every 30 minutes when it opens in November.
The gallery is allowed to let in 230 people every 30 minutes under health and safety legislation.
A document issued by the gallery explaining access to the show states: "This will mean that although the exhibition will be busy, it will be steady and not overrun at key times."
The move is a response to so-called blockbuster exhibitions which create vital revenue for museums and galleries but are often criticised as being too busy.
Gallery director Nicholas Penny said: "We've looked hard at the problems caused by very popular exhibitions in recent years and decided to take action ahead of what is likely to be one of the most important shows in our history.
"However, there are limits to what can be done - a drawing with exquisite detail for example is best looked at by one or two people at a time whether it is in a small or a huge exhibition space."
The exhibition includes more than 60 paintings from da Vinci's time working as a painter at the court of the ruler of Milan.
It was during his time in the city that he painted The Last Supper, a copy of which will be on show in the exhibition.