Abstract: In order to establish a relationship between caffeine and serum and urinary electrolytes, 30 healthy males were given an oral dose of 400 mg caffeine over a period of 120 min in four divided doses and electrolyte concentrations were measured during control and experimental periods. Serum potassium decreased significantly(P<0.01) from 4.4±0.2 (control period) to 3.9±0.2 (experimental period at 400 mg of caffeine). Increased urinary sodium (i.e from 139±3 in the control period to 209±8) and increased chloride concentrations (i.e from 46±7 in the control period to 124±9) associated with increased urinary output was noticed significantly(P<0.01) at 400 mg of caffeine. These results helps in establishing a dose response relationship between caffeine and electrolytes.