Protocol for development of the In-Vitro Critical Appraisal Tool (IV-CAT), intended to help ensure comprehensive and exacting peer-review of in vitro toxicology studies, and contribute to improving the quality of published in vitro research. In vitro studies are becoming an increasingly important source of data in chemical risk assessment. There are concerns, however, about the methodological quality of these studies and multiple interventions are being undertaken to assess and improve them. Interventions to improve study quality can focus on three target groups: (1) researchers designing, conducting and reporting primary in vitro exposure studies, (2) peer reviewers of journals advising on whether to publish a submitted manuscript and (3) authors of systematic reviews aiming to assess the risk of bias/study quality of the primary in vitro studies included in their review. Given that there are already interventions available or being developed for target groups (1) and (3), IV-CAT focuses on target group (2).