Single oral doses of the non-opioid, centrally-acting analgesic flupirtine maleate (Katadolon(R), CAS 75507-68-5) were administered to healthy volunteers and the 2 h plasma levels determined with a new specific HPLC assay. 50, 100, 200, and 300 mg were ingested as the commercial capsules in a double-blind randomized cross-over design with time intervals of at least 6 d Dose-proportionality was observed for the median 2 h plasma levels which is in agreement with dose-proportionality previously described for multiple-dose studies.