Since MMP they have become relatively rare, as Parliament has been heavily stocked by list MPs, who are simply replaced from the next on their party list.
Recent by-elections:
1993 - Tauranga
Winston Peters quits National and Parliament to contest the by-election as an independent.
No major party takes part and Mr Peters' high profile and opposition to an unpopular government sees him romp home with more than 90 percent of the vote. The McGillicuddy Serious Party, a joke party, comes a distant second. Mr Peters later forms New Zealand First.
1994 - Selwyn
After being sacked as finance minister Ruth Richardson quits Parliament and a fierce contest takes place to replace her. National's David Carter wins, but only by around 400 votes over the Alliance's John Wright. Labour came a distant third.
1998 - Taranaki-King Country
Jim Bolger quits Parliament after Jenny Shipley takes over as prime minister in a coup. His majority of more than 10,000 is slashed to 998 as National's Shane Ardern clings on to the seat from ACT's Owen Jennings. Labour come third, the Alliance fourth.
2004 - Te Tai Hauauru
Tariana Turia quits Labour and Parliament over the government's foreshore and seabed policy. Labour does not take on her or her new Maori Party and Mrs Turia walks home on a low turnout.
