Workers engaged in manufacture and use of dynamite experience acute toxic reactions with headache during work, weakness at the end of the working day, tachycardia and hypotension. Sudden death has been reported in dynamite workers after 2-4 days freedom of exposure, possibly due to rebound vasoconstriction resulting in acute hypertension or myocardial ischemia. In the present study 12 volunteers were examined before and during GTN exposure. Most of them experienced headache during work, and a slight but significant rise in heart rate and a fall in systolic blood pressure was found. In serial blood samples from cubital vein very high concentrations of GTN were detected. These high values can be explained by local absorption through the skin of the hand and the lower arm, and do not reflect the mixed venous plasma concentrations. Great interindividual variations were found in GTN plasma concentrations during work, probably indicating different working habits.