The research reported in this paper investigates the reasoning (or arguments) 'behind' intuitive judgements on risks of genetically engineered products. Each participant of the study (N = 72) was asked to rate two products out of a list of 12 genetically engineered products (which were selected from two fields of application for genetic engineering: medicine and foodstuffs) with respect to its risks. The subjects were asked to describe the reasons for their risk judgements out loud. An analysis of these arguments indicates that the participants gave very different reasons for their risk judgements, but that these can be reconstructed to form a manageable set of reasoning patterns. Important categories consist of reasoning patterns referring to the assessment of one's own or other people's knowledge and to the consequences which may result from genetically engineered products. Benefit-related reasoning patterns referring to beneficial aspects in assessing the risks also play a specific, although more limited role.