OBJECTIVE To establish a HPLC method for the determination of MMDL(1-methyl-10α-methoxy-9,10-dihydrolysergol) in plasma and study the relative bioavailability of domestic and imported nicergoline capsules.METHODS MMDL were extracted from plasma sample with dichloromethane(including 10% isopropanol) and separated on a Diamonsil C₁₈ column(4.6 mm×200 mm,5 μm).The mobile phase consisted of acetonitrile-20 mmol·L^-1 potassium dihydrogen phosphate(22∶78),the flow rate was 1 mL·min^-1,and methocarbamol was used as the internal standard.A single dose of 60 mg of domestic or imported capsules was given to 18 healthy volunteers in a randomized crossover study.MMDL concentrations in plasma was determined by the developed HPLC method,and then the pharmacokinetics and bioavailability were studied.RESULTS MMDL was separated well from other metabolites and endogenous substance,the standard curve was linear(r=0.999 7) within the range of 1.7 to 207 μg·L^-1 for MMDL.The main parameters for MMDL were as follows: ρ_max(97.9±54.6) and(103.0±60.5) μg·L^-1,t_max(1.2 ±0.4)and(1.2±0.4)h,t_1/2(3.7±2.6)and(4.0±3.0)h,AUC_{0→12 h}(283.7±218.4) and(305.3±244.6)μg·h·L^-1 respectively.The relative bioavailability of domestic to imported capsules was(93.8±6.4)%.CONCLUSION The established HPLC method was accuracy and sensitive for assay of plasma MMDL concentration.And the concentrations of MMDL in plasma were suitable for the bioavailability evaluation of nicergoline capsules.The results of statistics showed there were no significant differences between two preparations,and bioequivalence was observed.