The role of lithium, arsenic & vanadium in human bio-chemistry illustrates clearly the dual nature of those trace elements which are both essential and toxic depend on their oxidation state and concentrations at which they are supplied. Each of three essential elements has three levels of biologic activity, trace levels required for optimum growth & development, homeostatic levels (storage levels) &toxic levels. Trace & Ultra-trace levels i.e. deficiency levels cause many diseases e.g. Lithium is an effective drug for bipolar disorder and helps to reduce the severity & frequency of Mania. The incidence rates of suicide, homicide and rape are significantly higher in countries whose drinking water supplies contain little or no lithium, on the other hand toxic symptoms of it is polyuria & renal failure. Vanadium in trace amount is important industrially, as a: biological nutrient, epidemiological preventive. Toxicant. Environmental pollutant & Occupational hearth hazard. It plays animportant role in prevention of heart disease. The determination of arsenic (III) and arsenic (V) in environmental and biological systems is of considerable current interest to scientists.