Background: NTBC (2-(2-nitro-4-trifluoromethylbenzoyl)-1,3cyclohexanedione) is the mainstay of treatment in tyrosinemia type 1 (HT 1). The recommended administration is to be carried out in two divided daily doses. Patients and Methods: We monitored plasma NTBC concentrations in a series of seven patients who were changed from a multiple dose to a single NTBC dose. Two additional patients were directly started on single dose NTBC after diagnosis. In three patients, studies on NTBC kinetics were performed over 6 and 24 hours, respectively. Results: Plasma NTBC concentrations did not significantly decrease in any of the patients after changing from multiple to single dose NTBC treatment. In fact, in one patient, a significantly lower NTBC dose was required after changing to a single dose indicating a better compliance.