Madopar HBS (125 mg) is a controlled-release dosage form with 100 mg L-dopa and 25 mg benserazide. The 'hydrodynamically balanced system' (HBS) used for this novel dosage form of Madopar is a dosage form which, when in contact with gastric fluid and after dissolution of the gelatine shell of the capsule, forms a mucous body and a bulk density of less than 1 and releases the drug(s) at a desired rate whereas the dosage form remains in the stomach for a prolonged period of time. Drugs--in the present case L-dopa and benserazide--are released through the hydrated layer by diffusion principle. This system is valuable for drugs which are soluble at lower pH. By varying the composition of the excipients, desired release rates can be achieved. The in vitro dissolution rate of Madopar HBS formulation is as follows: L-dopa t75% = about 6 h and benserazide t75% = about 4 h. The floating behavior was tested in an in vitro test. These in vitro floating properties could be confirmed in man and were investigated in 10 healthy volunteers by means of gamma camera measurements using a poly-marker technique carried out in connection with a Valium CR study. It is expected that this novel drug delivery system proffers a valuable dosage form which delivers the drug at a specific rate allowing a better control of fluctuations in parkinsonian patients.