The neuronal ceroid lipofuscinoses (NCLs) are a group of genetically inherited lysosomal neurodegenerative diseases characterized by the intracellular accumulation of autofluorescent lipopigment storage material that causes progressive neurologic degeneration in all age groups. They belong to the group of lysosomal storage disorders. The clinical course includes progressive dementia, seizures, progressive visual failure (except in the adult-onset forms), and often movement abnormalities. Collectively, these disorders are the most common cause of an inherited childhood neurodegenerative disease and are increasingly recognized in late-onset or adult-onset forms. Classic infantile CLN1 disease is caused by an alteration in the PPT1 gene. It is a genetic disorder with an onset of symptoms between 6 and 24 months of age, with recorded later presented CNL1 diseases, juvenile and early adult. Symptoms may include signs of intellectual and motor decline including delays in reaching developmental milestones (development delays), twitching or jerking of muscles (myoclonic jerks), and seizures. Early diagnosis of CLN1 (neuronal ceroid lipofuscinoses type 1) disease is crucial to ensure optimum care for patients and their families. CLN1 disease is diagnosed by measuring the activity of the enzyme PPT1. This enzyme is necessary for the proper functioning of lysosomes. The function of this lysosomal thioesterase is to remove the fatty acids bound by thioester bonds to cysteine residues in proteins. In this study, the aim is to introduce a method for measuring the activity of an enzyme palmitoyl protein thioesterase 1 in a sample of leukocytes isolated from whole blood. An in house fluorimetric method was used to determine the activity of an enzyme palmitoyl protein thioesterase 1 in leukocytes isolated from EDTA whole blood. This method has proven to be sufficiently reliable for use in selective laboratory diagnostics after clinical suspicion of CLN1 has been established. However, as the fluorimetric method itself has many limitations and drawbacks, it is recommended that the first method of screening is the method of measuring PPT 1 activity from a dry drop of blood sample on filter paper.