Voting is under way in the by-elections triggered by the premature deaths of MPs Peter Law and Eric Forth.
The votes were triggered by two untimely deaths
South Wales seat Blaenau Gwent is up for grabs after independent MP Mr Law died from a brain tumour in April.
Conservative Mr Forth died of cancer last month, prompting a by-election in Bromley and Chislehurst.
Polling stations opened at 0700 BST and are due to close at 2200 BST with the results expected to be declared for both contests early on Friday morning.
Voters in Blaenau Gwent are also choosing a new Welsh Assembly member after Mr Law's death.
Weather around Blaenau Gwent is forecast to be moderately sunny all day. The forecast is for it to be sunny and warm in Bromley and Chislehurst.
The candidates in Bromley and Chislehurst are:
Ben Abbotts (Liberal Democrat)
Anne Belsey (Money Reform Party)
John Cartwright (Monster Raving Loony Party)
Nigel Farage (UK Independence Party)
Ann Garrett (Green)
Nick Hadziannis (Independent)
John Hemming-Clarke (Independent)
Bob Neill (Conservative)
Rachel Reeves (Labour)
Steven Uncles (English Democrats)
Paul Winnett (National Front)
The candidates in Blaenau Gwent are:
Dai Davies, Independent
Alan Hope, Official Monster Raving Loony
Amy Kitcher, Lib Dem
Steffan Lewis, Plaid Cymru
Owen Smith, Labour
Margrit Williams, Conservatives
There is also a by-election taking place for the Blaenau Gwent Welsh Assembly seat. The candidates are:
Steve Bard (Liberal Democrat)
John Burns (Conservative)
John Hopkins (Labour)
Trish Law (Independent)
John Matthews (Green)
John Price (Plaid Cymru)