The necessity of personal explorations among the still unwritten languages of cognate tribes soon made itself evident. In 1838 he joined a medical fellow student, Dr. Ehrström, in a journey through Lapland. This was the first of the voyages Castrén undertook in order to investigate the kinship between Finnish and several other languages. Following this he was appointed in 1840 to associate professor in Finnish and Norse languages at the University of Helsinki. In the following year, he traveled in Karelia at the expense of the Literary Society of Finland.