Following a dispute with Eck, he left for Wittenberg, where he taught mathematics at the private school of Melanchthon.
[1] Borrhaus travelled in the company of Felix Manz through Switzerland, Austria, Poland and Prussia.
Under the influence of Wolfgang Capito, Borrhaus published his first work, "De operibus Dei" 1527.
In 1541, his friend Simon Grynaeus arranged for Borrhaus a position teaching philosophy at the University of Basel, and then in 1544 he became professor of Old Testament and 1546, 1553 and 1564 served as rector.
Borrhaus associated with the advocates of tolerance Sebastian Castellio, Celio Secondo Curione and Michael Servetus.