The investigation includes two phases: - Phase I: the objective is to identify an assigned cause linked to a laboratory issue or not. If no assigned cause is found, the investigation must continue with Phase II (Figure 1) of this document. For the failure investigation, consult Annex 3.1 - Phase II: describes how results from initial and repeat testing can be evaluated in order to reach a consistent conclusion on the sample (Figure 2). The Phase II described in this Annex is not applicable to pharmacopoeial tests (dissolution test, uniformity of content, etc.) for which the conditions for repeating the test are given in the compendial text. It is recommended to identify each OOS investigation.