Holck presently participates in international collaborative work with:
- Prof. Jesse Byock, UCLA, USA
- Prof. Phillip Walker, UC Santa Barbara, USA
- Prof. Douglas Price, University of Wisconsin, USA
- Prof. Richard Steckel, University of Columbus, Ohio, USA
- Prof. Göran Possnert, University of Uppsala, Sweden
- Locally, Holck is also working together with the group of Prof. Erika Hagelberg (Biological Institute, University of Oslo), Prof. Torleiv Rognum (Forensic Medicine and Drug Abuse Research, Norwegian Institute of Public Health) and Prof. Jan Bill (Museum of Cultural History, University of Oslo).