Eighty cases of laboratory infection observed in our institute during 25 years were summarized. They were mostly research workers. Cases include not only manifestation of disease but also incidence of allergic responses. Causal agents were viral 22, rickettsial 14, bacterial or fungi 33, and toxin 11. Air contamination was considered to be the main cause of the above biohazard. Therefore, most of those accidents must be avoided by careful installation of the laboratory. Special attention should be given in laboratories where field specimens are treated and experimental animals housed. It was pointed out that most of the autopsy halls in Japan are little equipped to protect biohazard.