In 1903, Krzhizhanovsky was a member of the organising committee for the 2nd Congress of the Russian Social Democratic Labour Party (RSDLP), in Brussels, at which the party split between the Bolshevik and Menshevik factions, and was elected in his absence to its Central Committee. He travelled to Geneva afterwards hoping to reunite the two factions, but realised that mutal hostility had risen to such a pitch that it was no longer possible. In 1904-5 he was involved in organising the 3rd Congress of the Russian Social Democratic Labor Party.
