The Northern Line between Morden and Kennington will be out of action this weekend due to upgrade works.
Transport for London said a rail replacement bus service would operate between Clapham Common and Morden, calling at Clapham South, Balham, Tooting Bec, Tooting Broadway, Colliers Wood and South Wimbledon.
Passengers are warned journey times could be increased by about 40 minutes.
Underground tickets will be valid on London bus routes.
For runners and officials taking part in the London Marathon on Sunday, free travel is available on the Tube and DLR if you present a race number or pass.
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