A by-election was held for the British House of Commons constituency of Penistone on 13 July 1978. The seat had become vacant on the death of the Labour Member of Parliament John Mendelson, who had held the seat since a by-election in 1959.
The result was a hold for the Labour Party.
| Penistone by-election, 1978 | |||||
|---|---|---|---|---|---|
| Party | Candidate | Votes | % | ±% | |
| Labour | Allen McKay | 19,424 | 45.5 | ||
| Conservative | I. Dobkin | 14,053 | 32.9 | ||
| Liberal | D. Chadwick | 9,241 | 21.6 | ||
| Majority | 5,371 | 12.6 | |||
| Turnout | 42,718 | ||||
| Labour hold | Swing | ||||
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