Abstract: A moist web of exposed and developed photographic film or photographic paper is continuously advanced through a drying unit wherein selected areas of the path for the web are monitored by devices which generate signals denoting the heat absorptivity of monitored portions of the web. Such signals are processed and utilized to regulate the intensity of heat which is emitted by batteries of heating elements at both sides of the path for the running web. This ensures that the less developed portions of the web are subjected to sufficient heating action and that the more developed portions of the web are not overheated. The monitoring can involve ascertaining the intensity of heat which has penetrated through successive portions of the running web and/or ascertaining the intensity of heat which is reflected by successive portions of the running web and issues from heating elements designed to emit heat of known intensity.