In response to the prevailing assumption that Soren Kierkegaard was the "dominant influence" on Barth's second edition of his commentary on Romans, Bruce L. McCormack has this to say,
"A significant group of scholars working in the field of "early Barth" research have concluded that Kierkegaard's contribution, while not insignificant, was of much more limited value than was once thought. [...] [T]he influence of Heinrich Barth and Franz Overbeck was more important than that of the Danish philosopher. Kierkegaard's role was limited to strengthening Barth's commitment to certain modes of thought whose real origin lay in the influence of the distinctive form of neo-Kantianism elaborated by Barth's philosopher brother Heinrich in the years immediately following the way, and to providing him with a number of categories which (once they had been transformed for Barth's strictly theological purposes!) could be employed in clarifying a point of view which would, for the most part, have been complete without them."
(Bruce L. McCormack, Karl Barth's Critically Realistic Dialectical Theology: Its Genesis and Development 1909-1936 [UK: Oxford University Press, 1995], p.217)