SummaryThree virus strains isolated from Ixodes putus ticks were shown to be related to, though not identical, with Uukuniemi virus by complement-fixation tests. No antigenic relations were detected in the cross-neutralization test performed with the virus isolated and Uukuniemi virus. Two virus strains were isolated in 1969 on Tyuleniy island, Zaliv Terpeniya (Patience Bay) of the Sea of 0khotsk (Sakhaiin region), one virus strain in 1970 on the Ariy Kamen' rock situated close to the Pacific coast of Bering island, Commodore islands (Kamchatka region). The isolated agent was named after Zaliv Terpeniya, the place of its primary isolation.