As part of its programme for the prevention of health hazards caused by industrial work substances, the Berufsgenossenschaft der Chemischen Industrie began in 1977 to investigate the toxicity of those existing substances which are in widespread use, have many different applica­ tions and are suspected of being possibly dangerous to health, in particular of having long-term effects on health. It is hoped by means of this testing to close gaps in our knowledge and to increase the scientific validity of the required risk assessments. The results of the toxicological investigations carried out by the Berufsgenossenschaft der Chemischen Industrie, and the resulting substance assess­ ments have been