Background: There are doubts wether generic medications have the same bioavailability and efficacy compared with the original drugs developed by pharmaceutical companies with research capabilities. Aim: To compare the pharmacokinetics and clinical (motor) responses of Sinemet<FONT FACE=Symbol>â</FONT> and Grifoparkin<FONT FACE=Symbol>â</FONT>(generic carbidopa/levodopa 250/25 mg) in patients with advanced Parkinson's disease. Patients and methods: Patients were randomly assigned to Sinemet<FONT FACE=Symbol>â</FONT> (15 patients 62±12 years old; mean disease duration 11±7 years) or Grifoparkin<FONT FACE=Symbol>â</FONT> (15 patients, 64±11 years old; mean disease duration 12±4 years) groups. Medication and food were withheld 12 h before the study. Fifteen blood samples were collected (starting 9 AM) immediately before (sample 1, t=0 min) and after (samples 2-15, t=20-360 min) oral administration of a single dose of Sinemet<FONT FACE=Symbol>â</FONT> or Grifoparkin<FONT FACE=Symbol>â</FONT>, and plasmatic L-DOPA was quantified using HPLC with electrochemical detection. Additionally, each patient was clinically evaluated every 20 minutes, using the tapping test and the unified Parkinson's disease scale Hoehn &amp; Yarh. Results: Tmax (time at which the maximal L-DOPA concentration was reached) were 69±12 min and 64±11 min for Sinemet<FONT FACE=Symbol>â</FONT> and Grifoparkin<FONT FACE=Symbol>â</FONT> respectively (NS). Cmax (maximal L-DOPA concentration reached) was 3161±345 ng/ml for Sinemet<FONT FACE=Symbol>â</FONT> and 3274±520 ng/ml for Grifoparkin<FONT FACE=Symbol>â</FONT> (NS). The t1/2 (half life time), CL (clearance) and volume of distribution (Vd) values calculated were 159±32 min, 51.7±5.1 1/h and 3.6±1.2 l/kg for Sinemet<FONT FACE=Symbol>â</FONT> and 161±48 min, 58.7±8 l/h and 3.0±0.7 l/kg for Grifoparkin<FONT FACE=Symbol>â</FONT> (NS). UPDRS-III value for the best "on state" and for the worst "off state" were 23±11 and 50±19 for Sinemet<FONT FACE=Symbol>â</FONT> and 20±7 and 46±13 for Grifoparkin<FONT FACE=Symbol>â</FONT> respectively (NS). Conclusion: the results obtained showed that both drugs are bioequivalent in patients with advanced Parkinson's disease (Rev Méd Chile 2003; 131: 623-631)