This research project was undertaken for the purpose of studying poisoning by metallic mercury among workers of an electric lamp factory located in S. Paulo (Brazil). 71 workers were investigated, of whom 61 (85.92%) were chronically poisoned. Exposure period ranged from 4 months to 30 years. The 57 (80.30%) of chronically poisoned workers showed poor psychomotor co-ordination, 56 (78.88%) showed neurological impairments, 51 (71.83%) decreases in memory capacity, 47 (66.20%) pathological findings in the clinical exam, 45 (63.38%) psychiatric disturbances and 37 (52.10%) poor performance in the concentration test.