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In a small company producing rotor blades for aviation from carbon composites, epoxy resins based on Novolac and isophorone diamine as hardener are used. Both compounds can be absorbed via skin contact and were shown to be strong skin sensitizers. As a part of risk assessment, the industrial physician prompted a biological monitoring to determine the internal exposure of the workers.6 workers were identified with potential contact to the hardener and resin. We have collected pre- and post-shift urine samples at the beginning and mid of the work week and analysed them for the concentration of isophoronediamine and bisphenol-f-diglycidylethermetabolites as biomarker for the hardener and Novolac via specific mass spectrometric methods.We detected isophoronediamine in almost all urine samples with post-shift-values significantly higher than pre-shift. Median urinary excretion of isophoronediamine over the workweek was 195 µg/g crea. (Monday pre-shift), 709 µg/g crea. (Monday post-shift), 573 µg/g crea. (Wednesday pre-shift) and 1319 µg/g crea. (Wednesday post-shift). Results for urinary bisphenol-f-diglycidylether-metabolites were several orders of magnitude lower and near the limit of detection (0.5 µg/L).We found considerable internal exposures to isophoronediamine in workers producing carbon composite rotor blades. Our results indicate a cumulating internal exposure over the work-week. One of the workers showed clinical symptoms of allergic contact dermatitis in the skin examination. Use of inappropriate gloves was determined to be the cause for these high exposures. Biological monitoring should be part of risk assessment of workers handling epoxy resins.