This thesis focuses on the asymmetrical mutual intelligibility relation of Danish and Swedish, combining production and perception of native and non-native sounds to investigate the role of lenition and phonetic dissimilarities between languages in mutual intelligibility. In the first chapter I give an outline of the previous literature on mutual intelligibility (section 1.1), lenition (section 1.2), and Danish intervocalic lenition (section 1.3). In chapter 2 I formulate research questions and hypotheses on the experiments, which I describe in chapter 3 and 4. Chapter 3 is a chapter on production, describing the phonetic analysis of Danish and Swedish sounds (more specifically: pre- and intervocalic stops) after which I formulate more detailed predictions on the subsequent chapter (chapter 4) on perception. In chapter 4 I describe a perception experiment with Danish and Swedish participants, of which I link the results with the results of the production experiment in the general discussion in chapter 5. This thesis shows that Danish intervocalic lenition is not a factor in the Danish-Swedish asymmetrical intelligibility relation. Furthermore, the results show that perception of non-native sounds seems to be guided by different mechanisms than perception of native sounds.