In his book Das Prinzip Verantwortung, published in 1979, the philosopher Hans Jonas argued that all existing approaches in philosophical ethics are inadequate, because they do not effectively address the serious issues caused by the rapid expansion of modern technology. He proposed a completely new approach to ethics based on the principle of responsibility. His book - among others - inspired a number of theologians in Germany and the USA to develop their own versions of a Christian ethics of responsibility. In this article Jonas's version of an ethics of responsibility and the attempt of the American theologian William Schweiker to develop a Christian version of such an ethics in close proximity to Jonas's are critically discussed. It is pointed out that Jonas does not succeed in making out a convincing case for elevating responsibility to the fundamental principal of ethics. It is also argued that Schweiker's ambivalent stance in this regard does not support his claim that Christian ethics, in order to adequately respond to the serious ethical issues of our time, should be developed as an ethics of responsibility. The question "Can and should Christian ethics today be developed as ethics of responsibility?" is therefore left open.