Grinding fluids usually contain ethanolamines and nitrite as anticorrosive agents; these are known precursors of N-nitrosodiethanolamine (NDELA). In a preliminary study, it was demonstrated that workers' exposure to NDELA can be monitored by urine analysis. In order to estimate total daily exposure, 12 workers in a grinding shop were investigated by a three-step biological monitoring programme, giving the following results: (1) after exposure-free weekends, no NDELA was found in urine; (ii) urine collected during working shifts contained NDELA in up to microgram/kg concentrations; (iii) total daily NDELA excretion in 24-h urines was up to 40 micrograms; (iv) the amount of excreted NDELA correlated with the amount of NDELA contamination in the grinding fluid; (v) NDELA seems to be accumulated in the body during the week; (vi) other workers in machine shops, like maintenance and transport workers, are also heavily exposed to NDELA.