PSSM is a common muscle disease of many horse breeds including Noriker and Haflinger. The gold standard in diagnosis of PSSM in horses is to show thepresence of amylase-resistant, PAS-positive, abnormal polysaccharide inclusions in skeletal muscle fibres. PSSM typ 1 is associated with a gain in function mutation of Glykogensynthase 1 (GYS1), PSSM 2 could not be linked to a mutation. For the PSSMtype 1 diagnosisa simple gene test suits, but PSSM type 2 can only be diagnosed by muscle biopsy. Moreover, forthe latter undisputable histological criteria must be respected before a reliable diagnosis can be made. Frozen sectionssuited for PAS staining after amylase pre-treatmentare the gold standard. Since theinter observer variance of counting fibre types and pathological inclusions of correctly handled samples is not known, this study aimedto test observers agreement ofthe quantitative parameters determined inPSSM sections.