As part of its programme for the prevention of health hazards caused by industrial work substances, the Berufsgenossenschaft der chemischen Industrie (BG Chemie) began in 1977 to investigate the toxicity of those substances which are widely used, have many different applications and are suspected of being dangerous to health, in particular those having long-term effects on health. The investigations consist of a literature search and - depending on the results - commissions of experimental studies. 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 toxicologi­ cal investigations carried out by BG Chemie, and the result­ ing substance assessments have been published in German since 1987 in the form of ''Toxikologische Bewer­ tungen" ("Toxicological Evaluations"). In order to make this useful information internationally available, the BG Chemie began in October 1990 to publish them as a book series in English, of which the fourth volume (containing 13 individual evaluations) is presented here. Because of the short time between publishing volume 1 , 2 and 3, printing of "Introduction" (consisting of a general overview of the programme, lists with names of people involved as well as substances under investigation) was abandoned in volumes 2 and 3. In this volume a revised "Introduction" is published presenting more detailed infor­ mation about the ongoing work. The publication of further individual evaluations and, if necessary, reassessments of previously published evalua­ tions is planned.