Mutagenic exposure conditions in several rubber manufacturing companies (n=9) in The Netherlands were studied. Mutagenicity of total suspended particulate matter in air (TSPM) and of wipe samples from possible contact surfaces were measured in the Ames mutagenicity assay with Salmonella typhimurium YG1041 in the presence of a metabolic activation system. Large differences in median mutagenicity of TSPM samples were observed between companies (range 49-1056rev/m(3)) and to a lesser extent between production functions (range 129-402rev/m(3)). The production function curing revealed overall the highest TSPM mutagenicity levels. Forty-one percent of the surface wipe samples revealed mutagenic activity ranging from 26 to 665rev/cm(2). Mixing had the largest proportion of positive samples resulting in a median surface mutagenic contamination of 39rev/cm(2). Surface mutagenic contamination, averaged per department/company combination, showed only a weak correlation with TSPM mutagenicity (r=0.28, P=0.05). Company, production function and total soluble matter (e.g. mass collected upon extraction with organic solvents with different polarity) explained 79 and 81% of the variability in mutagenicity of TSPM and surface contamination levels, respectively. "Company" was identified as the most important exposure determinant for mutagenic activity in TSPM and surface wipe samples. This indicates the importance of company specific determinants like production volume and rubber chemicals used for the encountered mutagenic exposure conditions. Detection of substantial mutagenic activity on possible contact surfaces supports furthermore the potential importance of the dermal route in the uptake of genotoxic compounds of workers in the rubber manufacturing industry.