Russian opposition leader Alexei Navalny was hospitalized after suffering an acute allergic reaction on Sunday.
He is serving a 30-day jail term for calling for unauthorized protests.
Opposition leader Navalny’s spokeswoman Kira Yarmysh wrote on Twitter that he was hospitalized on Sunday morning.
She said the cause of Navalny’s allergic reaction was unknown.
Police rounded up more than 1,000 people in the Russian capital at the march on Saturday.