In December 1992 the IAEA convened an advisory group meeting with the aim of recommending a set of unconditional exemption levels relevant to solid materials contaminated with, or containing, radionuclides (now called clearance levels). This paper will report on the results of that meeting. It will describe the methodology used to derive clearance levels from the results of radiological assessment studies related to landfill disposal and incineration of wastes and to the recycling and reuse of metals and concrete. It will also recall the general exemption principles and explain the change of terminology in the light of the IAEA Basic Safety Standards, which are currently under revision. Finally, the recommended clearance levels will be discussed in the framework of a regulatory system. (author). 17 refs, 1 fig., 3 tabs.