There is widespread agreement that the potential of gene therapy was oversold in the early 1990s. This study, however, comparing written material from the British, Danish and German gene therapy discourses of the period finds significant differences: Over-optimism was not equally strong everywhere; gene therapy was not universally hyped. Against that background, attention is directed towards another area of variation in the material: different basic assumptions about science and scientists. Exploring such culturally rooted assumptions and beliefs and their possible significance to science communication practices, it is argued that deep beliefs may constitute drivers of hype that are particularly difficult to deal with. To participants in science communication, the discouragement of hype, viewed as a practical–ethical challenge, can be seen as a learning exercise that includes critical attention to internalised beliefs.