Background: This work presents intentional use of harmful biological agents based on the National Register of Biological Agents (in Polish abbreviated as KRCB) as of July 2020. Material and Methods: Generally, KRCB is a central database gathering notifications of intentional use of biological agents classified as risk groups 2–4 at work. Results: Notifications were sent by 672 enterprises, including for diagnostic – 63%, research – 30% and industrial purposes – 7%. The largest number of notifications were sent by hospital-based diagnostic laboratories – 34%, laboratories other than hospital-based – 34%, and higher education and research units – 15%. In total, 7077 workers (88% women, 12% men) were exposed to biological agents intentionally used at work. The following bacteria were most frequently used: Escherichia coli (with the exception of non-pathogenic strains) – 4394 (62%) exposed workers, Staphylococcus aureus –4122 (58%), and Pseudomonas aeruginosa – 3726 (53%). Biological agents recognized by the International Agency for Research on Cancer as carcinogenic were used in 107 enterprises (16%), including the following viruses: hepatitis B virus (HBV) – 25 enterprises (4%), hepatitis C virus (HCV) – 24 (4%), human immunodeficiency virus type 1 (HIV-1) – 18 (3%), Epstein-Barr virus (EBV) – 10 (1%), human papilloma virus (HPV) – 5 (1%), human herpes virus type 8 (HHV-8) – 3 (<1%), human T-lymphotropic virus type 1 (HTLV-1) – 3 (<1%), as well as bacteria Helicobacter pylori – 18 (3%) and parasites Schistosoma haematobium – 1 (<1%). Conclusions: While KRCB is a unique source of information on biological agents intentionally used in workplaces, it also provides an important link in the chain of information on occupational exposure to harmful agents in Poland. Med. Pr. 2021;72(2):131–43