Historically biological monitoring to assess exposure has been difficult due to the rapid half-life of NG. However, the recent development of a method to assess NG and its metabolites (glycerol dinitrates, GDNs) in urine has made biological monitoring more feasible. The data reported here result from samples taken from three sites using NG. Two of the sites are munitions manufacturing sites and the other site is a pharmaceutical manufacturing site. The range of urinary GDN concentrations found in the samples at the two munitions sites were 0.9-18, and 0-4.7 micromol/mol creatinine, and at the pharmaceutical site were 0-0.9 micromol/mol creatinine). The presence of nitroglycols in the urine of workers despite the use of personal protective equipment and local exhaust ventilation shows the usefulness of biological monitoring to assess the efficacy of any controls in place and the potential of dermal absorption of NG.