This study advances our understanding of why and how the performance of standardized safety routines varies. Based on six months of field research and interviews in a molecular biology laboratory, this study examines the divergence of safety regulations and actual routine performance. It identifies distinct routine components that address different aspects of safety. While safety regulations and training aim at preventing adverse effects of hazardous substances on the scientists, the scientists are concerned about potential contamination of their experiments. This study investigates the relationship between organizational and scientific objectives. It argues that organizational objectives fall behind scientific objectives in safety routine performance to the extent that their pursuit requires a set of actions separate from those actions that suffice to meet the scientists' professional concern. © The Author(s), 2009.