Abstract: Method and apparatus for recording sweat gland activity which provides a pictorial representation thereof by physical contact of an iodide treated skin area with a dry sensitized substrate. In one preferred embodiment, the sensitized substrate comprises a sheet material which has been coated with an aqueous solution containing from 1 to 10 percent by weight of starch and from 2 to 10 percent by weight of a suitable oxidizing agent such as potassium persulfate. Alternately, the dry sensitized substrate comprises a starch-oxidizing agent mixture which has been impregnated into an absorbent base layer. With slight modification of the foregoing embodiment, the present invention also provides a method and apparatus for obtaining inkless fingerprints by forming a sensitized coating in situ on a substrate. For fingerprinting purposes, the sensitized coating is preferably formed from a quick drying starch-oxidizing agent solution including alcohol as a solvent.