High stakes in SA by-election

When voters in the Adelaide seat of Fisher last elected a new MP, Bob Hawke was prime minister, the VN Commodore was rolling off production lines and a young Steve Waugh led the Aussies to victory in the Ashes.

A quarter of a century later, voters will go to the polls for a by-election to replace long-serving MP Bob Such.

Elected in 1989 as a Liberal MP but independent from 2000, Dr Such died in October after being diagnosed with a brain tumour.

Saturday's Fisher by-election is shaping as a three-horse race with consequences for the parliamentary balance of power.

Labor holds 23 of the 47 lower house seats and governs with the support of independent cabinet ministers Geoff Brock and Martin Hamilton-Smith.

The Liberals holds 20 seats, with a by-election planned for the vacant seat of Davenport next year.

If Labor wins Fisher, it will have a lower house majority for the first time since Premier Jay Weatherill scraped to power at the March state election.

A Liberal victory would boost the opposition's chances of challenging legislation and bolster the leadership of Steven Marshall.

Fisher is considered to be relatively safe Liberal territory, having been held by Labor for just one term since 1970.

Liberal candidate Heidi Harris has campaigned heavily on unpopular state budget measures, including a big increase to the emergency services levy.

But Labor remains hopeful its candidate, anti-violence campaigner Nat Cook, will benefit from the unpopularity of the federal coalition.

It has deployed posters highlighting federal spending cuts and uncertainty about the government's promise to build submarines in Adelaide.

The Liberals have, meanwhile, targeted independent candidate Daniel Woodyatt, who has the backing of Dr Such's wife and appears likely to attract strong support.

Mr Woodyatt, a lawyer with the Crown Solicitor's Office, says he hopes to continue the independent legacy of Dr Such.

Liberal posters have questioned Mr Woodyatt's independence, highlighting his one-time Labor Party membership and previous endorsement of the premier.