An RP-LC method for the determination of melatonin with UV detection at 223 nm was developed and validated using a C(18) column at 25 A degrees C as stationary phase and a mixture of 0.1 M triethylammonium acetate at pH 7.0, and acetonitrile (70:30, V/V) as mobile phase. The method was linear (R (2) = 0.9997) over the concentration range of 0.05-8.00 mu g mL(-1). The RSD% of intra- and inter-day precision studies were less than 2% while the recovery% values were between 99 and 101%. The detection and quantitation limits were 9 and 31 ng mL(-1), respectively. The method was found to be specific, accurate, precise and sensitive for the determination of melatonin from chitosan nanoparticles.