In an epidemiological study of 286 metalworkers exposed to metalworking fluids (MWF), the prevalence of contact sensitization was investigated. In part I, irritant contact dermatitis in metal workers has been discussed. In 40 employees with dermatitis, patch tests were performed with a routine series, a series of common components of MWF, and a series of preservatives the employees worked with. Contact sensitization was established in 8 persons (2.8% of all workers), of whom 4 were allergic to biocides and/or corrosion inhibitors. Difficulties in interpretation of the relevance of positive reactions are discussed. Attention is paid to the use of biocides in MWF, their various types and their sensitizing capacities. Measures to reduce the induction of contact sensitization to preservatives in water-based fluids are discussed.