The paper deals with properties of structured procedures from a mereological point of view, i.e. with respect to their constitutive elements. As a result, it is argued that procedures amount to structured complexes (wholes) made of uniquely determined parts and that the part-whole relation is of the partial-ordering type. However, such a mereology is not a standard one: the principle of extensionality and the idempotence law do not hold there.