The Scottish National Party and the Scottish Conservatives have launched their campaigns for the Livingston by-election.
Angela Constance was chosen to be the SNP candidate
SNP candidate Angela Constance said she would fight on issues such as hospital provision and fire service cover.
Conservative candidate Gordon Lindhurst called for a challenge to Labour dominance in Scotland.
The by-election, set for 29 September, has been caused by the death of former Foreign Secretary Robin Cook.
Labour has selected Mr Cook's election agent and friend Jim Devine.
The Greens are fielding former biology teacher David Robertson, who is employed by the Action on Smoking and Health campaign.
Gordon Lindhurst called for a challenge to Labour dominance
The Scottish Socialist Party, which achieved less than 2% of the vote in May, named Steve Nimmo, the party's regional organiser for the Lothians, as its candidate.
UKIP chose former army officer Peter Adams and the Liberal Democrats nominated Charles Dundas.
Mr Cook had a majority of 13,000 in May's general election.
SNP candidate Ms Constance, who came second to Labour at the general election, said: "Together we can secure the future of St John's (Hospital), reverse the proposed cuts in fire cover and ensure that Tony Blair wakes up on the last day of the Labour Party conference with a huge electoral hangover."
SNP leader Alex Salmond claimed the vote was an opportunity to push the independence agenda.
He said: "SNP by-election victories always move Scotland forward. That's what happened in Hamilton and in Govan."
Mr Lindhurst, an advocate in West Lothian, said the people of Livingston were suffering under a one-party state, with Labour in power at local, Scottish and UK levels.
Meanwhile, millionaire businessman Charan Gill has been ruled out as a Labour candidate in the Cathcart by-election which is being held on the same day.
The founder of the Ashoka restaurant chain, known as the "curry king", will not stand in the election which was called following the resignation of Lord Watson.
The MSP stood down after he admitted setting fire to curtains at the Prestonfield Hotel.
Mr Gill, 50, who is understood to have had the backing of First Minister Jack McConnell, is a long-term supporter of the Labour Party but only joined this week.
Labour's National Executive Party is understood to have ruled he could not stand.
Mr Gill's interest in the Glasgow seat provoked a backlash among local activists who felt the Labour hierarchy was trying to parachute in a rookie candidate.
He said he was "very disappointed".
The four names on the Labour shortlist are three city councillors Charles Gordon, Archie Graham and Irene Graham - together with Manjinder Singh, a business analyst with Scottish Power.
The party will make its final selection on Friday.
Scottish National Party leader Alex Salmond said of Labour: "Their whole by-election plan is in tatters, which is no surprise because everything Mr McConnell puts his fingers on usually collapses or turns to dust."
The SNP is also expected to determine its shortlist for Cathcart onnWednesday evening, with the candidate due to be unveiled on Friday.