The invention relates to an in vitro process for determining the functional IL-17 pro-inflammatory dependent level (IPDL) of a biological sample, comprising the following steps: a) measuring the level of an inflammatory marker produced by IL-17-sensitive cells incubated in the presence of a biological sample, b) measuring the level of said inflammatory marker produced by said cells incubated in the presence of a biological sample, in the presence of antibodies which neutralize the biological activity of IL-17, and c) determining the IPDL level, which is the difference between the level of said inflammatory marker measured in step a) and the level of said inflammatory marker measured in step b).