The public controversies associated with biotechnological progress (genetic modification, cloning, and so forth) increasingly impact upon biology teaching in school; teachers find themselves engaged in discussions with pupils on value-laden issues deriving from the social and ethical implications of the 'new science'. The research described in this paper focused upon the thinking of a sample of 41 biology teachers as they endeavoured to implement the first year of the new Scottish Advanced Higher Biology course and to face the challenges associated with these controversies. Following questionnaire returns, the investigation employed semistructured, in-depth interviews with 10 teachers and, separately, with their 61 pupils (17-18 years of age) and was part of a medium-term to long-term evaluation of a university summer school that had endeavoured to update these teachers on recent biotechnological advances. While teachers were found to be fairly positively disposed to handling discussion of such contentious matters, they were none-too-clear as to its precise merits and functions; many lack confidence in handling discussion. The research indicates that much needs to be tackled by way of professional development for science teachers now engaged in dimensions new to science teaching.