Drawing on the work of Bernadette Bensaude-Vincent and Isabelle Stengers on the history of chemistry, this article develops the idea that drug molecules can be understood as ‘informed materials’. This study argues that molecules should not be viewed as discrete objects, but as constituted in their relations to complex informational and material environments. Through a case study of commercial pharmaceutical R&D, the article examines the role of combinatorial and computational chemistry in enriching the informational and material environment of potential drug (...) molecules. Within the contemporary pharmaceutical laboratory, experiments on molecules can be conducted not just in vitro and in vivo but also, according to researchers, in silico. Molecules come to exist not just as physical reagents but also as elements of arrays, libraries and databases of other molecules, and in a virtual form in computer simulations and virtual libraries. Molecules are also understood by researchers to exist in a ‘chemical space’ of other different molecules, where the notion of chemical space is used both to refer to differences in molecular structure and to territories owned or occupied by particular firms. The article argues that pharmaceutical companies do not merely discover molecular structures that potentially could exist, but also invent novel forms of chemical entity. (shrink)