An attempt has been made to determine, on films prepared from aqueous polymeric dispersions, the time needed after casting for the films to be fully formed. Methods such as measuring the tensile strength, the elution of water-soluble matter, several methods of measuring the glass transition temperature and measurement of the proton relaxation time by nuclear magnetic resonance were used. It was found that measurements of water absorption and water-soluble material elution gave the same estimates of film-forming time, while tensile strength reached stability sooner; other methods gave no useful indication of the time for film formation. -- AATA