There, she met with the future director of the St. Petersburg Pedagogical Institute, Theodor Johann von Middendorff (1776–1856), whose father was a Baltic German pastor in Karuse, Estonia.

Due to stormy conditions, the expedition failed to reach Novaya Zemlya, but Baer and Middendorff explored Russian and Norwegian Lapland, as well as the Barents and White Seas.

From 1843 to 1845, Middendorff travelled with these instructions, to the Taymyr Peninsula and then along the coast of the Sea of Okhotsk and entered the lower Amur River valley (which at this time was Chinese territory).

He published his findings in Reise in den äußersten Norden und Osten Sibiriens (Travels in the extreme north and east of Siberia) in German (1848–1875), which included an account of the effects of permafrost on the spread of animals and plants.

He also wrote Die Isepiptesen Russlands (1855), an account of bird migration in Russia, and a monograph on molluscs, Beiträge zu einer Malacozoologia Rossica (1847–1849), in which he coined the term radula.Baer's expedition instructions had the German title „Materialien zur Kenntniss des unvergänglichen Boden-Eises in Sibirien“ (=materials for the knowledge of the perennial ground ice in Siberia).

The text is introduced with detailed comments and references on additional 66 pages written by the Estonian historian Erki Tammiksaar.

Middendorf died in 1894 at Hellenorm, Kreis Dorpat, in Governorate of Livonia, Russian Empire (now Valga County, Estonia).