A method of sensing the concentration level of at least one particular
electrolyte in the sweat fluid of a subject, includes providing a sweat
sensor system having sweat fluid absorbing material, measuring apparatus
for sensing the electrical conductivity of sweat fluid absorbed by the
absorbing material and producing ionic concentration data for said at
least one particular electrolyte, and a user interface connected to the
measurement apparatus for interpreting the data to a user. The absorbing
material is applied to the skin of the subject to cause sweat fluid
thereon to be absorbed by the absorbing material whereby the measurement
apparatus produces ionic concentration data for the sweat fluid absorbed
and the user interface interprets the data for a user.