His book "The Kurbskii-Groznyi Apocrypha: The Seventeenth-century Genesis of the 'Correspondence' Attributed to Prince A. M. Kurbskii and Tsar Ivan IV" (1973) claims these letters are forgeries.
* The Kurbskii-Groznyi Apocrypha: The Seventeenth-century Genesis of the 'Correspondence' Attributed to Prince A. M. Kurbskii and Tsar Ivan IV, 1971* Russian political folkways // Russian Review, Vol.