Abstract A new suggestion for the definition of pressure drop is submitted which was accepted by the ISO/TC126-SC1 committee and Coresta Technology Study Group. The various standard conditions under which the pressure drop is to be measured are substantiated individually. The suggestion is based on a thorough study of the literature (state 1976), which is cited, with sources. This report was published in English and French in: Coresta Information Bulletin 1977-1, 17-33.