Inorganic arsenic and its methylated metabolities were measured in 108 spot urine samples obtained from the medical surveillance programme of workers exposed to inorganic Arsenic in July 2006. 15% of the samples showed levels higher than limit value of 35 microg/L (mean value 23,9 microg/L). After the improvement of the working conditions, in August-October 2006, we collected a urinary sample from each of the 108 workers enrolled. A questionnaire was also administrated, in order to investigate the influence of occupational and non occupational factors on the urinary arsenic excretion. The median value of urinary arsenic was 15,12 microg/L; among the 108 samples, 5% showed levels higher than limit value. A significant difference was observed in relation with sea-food consumption and aging stratification. In conclusion, we have described a significant reduction of urinary arsenic excretion between the two phases of biological monitoring, likely due to a proper hygienic work-related intervention.