Naturally occurring arsenic in ground water has been a recognised serious hazard in many parts of the world in general and in some south Asian countries in particular. Recently, ground water arsenic contamination has been documented from various parts of Pakistan. In this study arsenic exposures and arsenic attributable health risks are estimated for two potentially impacted areas in Pakistan. The use of early stage biomarkers as proxies for exposure has also been tested from a well characterised field area in West Bengal and their utility to studies in northern Pakistan indicated.In this thesis, an arsenic exposure and risk assessment study was carried out in Allama Iqbal Town Lahore, Pakistan and a preliminary exposure survey carried out in the Peshawar basin, Khyber Pukhtoon Khwa, Pakistan. The major identified exposure routes in both areas was found to be ground water, used for drinking/cooking purposes, and to a lesser extent raw rice. In Allama Iqbal town a median arsenic contamination of 24 µg/L (with maximum value 960 µg/L) in drinking water/cooking water (n=132) derived from ground water sources was found and which is well above the 10 µg/L arsenic WHO provisional guideline value. Rice arsenic concentration (n=86) had a median value of 0.08 mg/kg (range 0 .03 - 0.25 mg/kg), of this 40% - 93% (median 69%) was inorganic. The calculated excess lifetime cancer risk value from drinking/cooking As contaminated water (3.30 × 10-3) and also from both water and rice together for volunteers of Allama Iqbal town Lahore, Pakistan is (3.52 × 10-3) higher than the (10-4-10-6) range typically used as a threshold value by USEPA. Factors such as variations in water and rice supply, diet, dietary pattern, genetics, age are in combination also important in determining human exposure and arsenic attributable health risks in this area. The maximum ground water arsenic contamination value (8 µg/L) found during the study of arsenic contamination in the Peshawar basin was lower than the WHO provisional guide vBiomarkers of arsenic exposure, viz. human hair (n=115), nails (n=144) (toe and finger nails), and urine (n=23) collected from Allama Iqbal town Lahore have a median value of As in hair 0.33 mg/kg (0.03 -14.7 mg/kg), As in nails 0.84 mg/kg (0.53 - 64 mg/kg) (mean 0.94) and for urine median 118 µg/g creatinine (19 - 350 µg/g creatinine) (mean 137 µg/g) for urine. Hair As has a significant correlation (r2=0.63 & p=0.01) with arsenic contents of drinking water as does to some extent nail As (r2=0.24 & p=0.05). Similarly chronic daily intake of water is positively correlated with As content of hair (r2=0.42 & p=0.01). This is also helpful in confirming ground water used for drinking /cooking as the major arsenic exposure route in this area.The biomarkers of arsenic exposure study when applied in West Bengal India gives highly significant association values (r2=0.70 & p=0.01) for cooked rice and chronic daily intake from cooked rice. With the frequent use of rice and being used as a staple food in West Bengal, ingestion of arsenic contaminated rice is being confirmed as a major exposure route in the West Bengal by the biomarkers of exposure: this is in contrast to Allama Iqbal town Lahore where drinking As contaminated water is being confirmed the major exposure route. ICP-MS was used for quantifying the total concentration of arsenic in hair, nails, water, rice and urine. IC- ICP-MS was used for arsenic speciation analysis of urine as well as raw rice. An informed consent based questionnaire survey was used for collection of relevant information.