A sensitive, reproducible and accurate high performance liquid chromatographic (HPLC) method for the quantitative determination of haloperidol in plasma has been developed and validated. Sample preparation involves extraction of haloperidol and diazepam (internal standard) from 0.5 mL plasma. The separation was carried out in a stainless steel, resolve C18column with a mobile phase composed of a mixture of 55% methanol and 45% HPLC water containing 0.2 M ammonium acetate and adjusted to an apparent pH 7.2. The mobile phase was pumped at a flow rate of 1.5 mL/min. The column oven temperature was adjusted at 38°C and the effluent was monitored at 249 nm. The retention times for the internal standard and haloperidol were found to be 5.1 and 6.3 minutes, respectively. Peak-height ratios of the drug to the internal standard were used for the quantification of haloperidol in the plasma samples. The average (±SD) absolute and relative recovery of haloperidol were 97±3.6% and 100 6±1.52%, respectively. The intraday coefficients of variation (CVs) ranged from 1.74 to 4.68%, while the interday CVs varied from 2.31 to 5.23%. The detection limit for haloperidol in plasma was found to be 5 ng/mL.