Measurements of hazardous substances in workplace atmosphere can be ca
rried out by external and internal measuring services. For internal me
asuring services the BG's supports a procedure in order to recognize t
he measured values. The procedure of founding an internal measuring se
rvice based on the criteria of TRgA 400 is described in details. An ef
fective support of the internal measuring services shall be reached in
following points: establishment of expert knowledge (training), quali
ty assurance, organisation of an information system and arrangement of
an exchange of experiences.