The risk posed to human health by environmental manganese (Mn) exposure is unknown. The purpose of this study is to establish if subclinical effects related to Mn exposure and examine the factors influencing psychoneurobehaviral outcomes of Mn exposed workers. This study involved 121 male workers of welding, alloy furnace, and manufacturing of welding stick. Study investigations include: a questionnaire covering demographic characteristics, job and exposure history and medical symptoms and conditions, monitoring workplace air for personal exposure to respirable and inhalable manganese, analysis of blood and urine samples. psychoneurobehaviral test(neurobehaviral core test battery (NCTB), signal change on magnetic resonance imaging (MRJ) scans, minimental state and neurological examination). The main results of this study were as follows: 1. Preliminary results showed that, with increasing manganese exposure, neurobehaviral performance was poorer and signal change on MRI scans increased. 2. The results of examination revealed significant relations on psychoneurobehaviral out-comes (neurobehaviral performance, signal change on MRI scans, and neurological features). 3. In multiple regression, age and educational status as demographic variables and exposure level were significantly related to 4neurobehaviral test. Also exposure level and serum Mn concentrations were positively relatel to signal change on MRI scans and neurological features affected by Mn on the brain (signal change). 4. Psychoneurobehaviral outcomes from Mn exposure were related to neurobehaviral performance, signal change on MRJ scans, neurological features and profile of mood states (POMS), and influnced positively with age, alcohol and smoking history, and duration of Mn exposure, negatively with educational status. Serum Mn concentrations in combination with brain MRI scans, and perhaps a battery of neurobehaviral tests, appear to be the best way to monitor excessive exposure to Mn. These results are consistent with our knowledge on Mn action on the brain and are similar to the type of neurobehaviral dysfunction. They suggest that there may be age, educational status, and life style (alcohol and drinking history) differences with chronic environmental exposure. These findings suggest further evaluation, particularly on relationships between Mn exposure, aging, and susceptibility factors.