The departure of John Finnie and Jean Urquhart leaves the Scottish National Party with 65 MSPs, and an overall majority in the Scottish Parliament of just one.
They were among eight Nationalist MSPs who led a grassroots revolt against the party leadership's plan to take an independent Scotland into Nato, the nuclear-armed military alliance.
The about-turn on the policy split the party when it was voted through, by 426 votes to 332, at the SNP conference in Perth last week.
Angus Robertson, the defence spokesman, was booed by some members as he spoke in favour of the new strategy.
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